Welcome and Starter
09:20 - 09:50 D. Dravins: Radial Velocities and Wavelength Shifts
Abstract: Motions in the radial direction carry names reflecting their measurement: Doppler shift from spectroscopy, redshift in cosmology or range rate for tracking spacecraft. From such measures, radial velocity is deduced, either absolute relative to some reference frame, or as a change over time or between locations. To reach the precision and accuracy required to find also small exoplanets, the observational process must be well understood. For determining radial motions of stars, displacements of spectral line wavelengths are measured relative to some laboratory standard. Issues arise in defining the meaning of wavelength since all spectral lines are somewhat asymmetric and in practice only their central portions can be measured. In deducing radial velocities, issues arise because spectral lines are formed in dynamic atmospheres, producing convective wavelength shifts. These differ between lines of different strengths, excitation and ionization levels, and change with stellar spectral type. They vary across stellar disks and are modulated by magnetic activity. Line asymmetries (and thus wavelengths) also depend on stellar rotation and spectrometer resolution. With further effects such as gravitational redshifts, this conspires to make spectroscopically deduced radial velocities differ from that of the stellar center of mass. Other determinations of stellar radial motions exist in astrometry. Stars in open clusters move with the same velocity vector. Parallaxes give distances, while proper-motion vectors show the fractional change with time of the cluster's angular size. This equals the time derivative of distance, yielding the radial velocity independent of stellar spectra. Differences between such astrometric velocities and apparent spectroscopic values may reveal lineshifts intrinsic to the stellar atmosphere.
09:50 - 10:20 A. Reiners: Detecting the solar system today
Abstract: Early expectations for extrasolar planetary systems were partly motivated by knowledge about the solar system. Until today, the discovered planets and planetary systems are vastly different from our home. Does this mean that we are living in a freak system or are our discoveries just the most unusual planets among a much larger mass of objects more similar to those orbiting the Sun? I will not be able to answer these question but set the stage for our Workshop on how the solar system fits into the exoplanet picture.
Observations of solar radial velocities until today
11:00 - 11:30 R. Haywood: What we can learn from the Sun?
Abstract: The Sun is the only star whose surface can be imaged directly, at high spatial and temporal resolution. We can use our Sun to probe the physical processes whose observational signatures undermine exoplanet discovery and characterisation. Much work has been done, both in photometry and spectroscopy, to identify the signatures of individual surface features directly in spatially resolved images, reconstruct their disc-averaged signatures and compare them to synoptic observations. These analyses inform our knowledge of solar magnetic fields, velocity flows and convection processes, which in turn constrains our theories of the Sun's interior structure and dynamo. This solar knowledge can guide our understanding of stars as a whole if we can identify and observe proxies for these processes on other stars (eg., Ca II H&K emission as a proxy for chromospheric plage). For the Sun, we have access to observables that currently remain out of reach for distant stars (eg. the total, absolute magnetic flux; the active-region filling fraction, etc.). We can study these observables on the Sun to identify additional proxies to further our knowledge of other stars. These solar investigations are key to discovering and characterising other planetary systems like our own, and will inform the design of the next generation of instruments for stellar and exoplanetary science.
11:30 - 12:00 D. Deming: The Apparent Velocity of Disk-integrated Sunlight: Lessons from the Early Years
Abstract: During 1982-93, with the essential collaboration of several colleagues, we began an effort to measure the stability of the apparent velocity of integrated sunlight, i.e., the Sun-as-a-star. We used the McMath-Pierce Fourier Transform Spectrometer (FTS) of the National Solar Observatory on Kitt Peak, at a wavelength near 2.3 micrometers. We measured 16 overtone lines of carbon monoxide, and 5 atomic lines, at a spectral resolving power of 400,000 and a signal-to-noise ratio of about 3000 in a 30 minute integration. The FTS is a Michelson interferometer, and we calibrated the wavelength scale using an absorption cell containing nitrous oxide at low pressure. The spectral calibration was stable in wavelength to much better than 1 meter/sec, and we were able to measure terrestrial winds across Kitt Peak from the wavelength shifts of telluric lines. Our principal source of error for the velocity of disk-integrated sunlight was the imperfection of the optical integration of the solar disk. Those imperfections were caused by spatial variations in both the telluric atmosphere and the beamsplitter of the interferometer. We defined and removed those effects by monitoring the measured velocity as a function of image rotation. We found that the integrated light velocity in these spectral lines, formed relatively deep in the solar photosphere, was correlated with the disk-averaged magnetic field signal as measured by a conventional longitudinal magnetogram. Based on that correlation, we concluded that the peak-to-peak velocity change over a solar cycle would be about 25 meters/sec. Since our 1994 paper, there has been new work using more modern methods, and the inferred amplitudes in optical lines are lower than we found in the infrared. Although the McMath-Pierce FTS is no longer operational, some valuable lessons from our early work remain relevant today. I will discuss those lessons in the context of current programs to monitor the velocity of disk-integrated sunlight, and eventually to detect terrestrial planets orbiting solar-type stars.
12:00 - 12:30 K. Strassmeier: PEPSI Sun-as-a-star spectra
Abstract: TBD
Stellar activity and RV jitter
14:00 - 14:30 N. Meunier: From the Sun to others stars: radial velocity time series for late-F to early-K old stars
Abstract: TBD
14:30 - 14:50 C. Watson: UnEarthing planets from the cloak of activity: Clues from the HARPS-N solar telescope?
Abstract: Stellar surface inhomogeneities (manifestations of which include spots, plage, convective blueshift suppression, and granulation) induce radial velocity (RV) perturbations that can mask or even mimic the Doppler wobble effect induced by an orbiting planet. Understanding and correcting for this stellar noise is crucial for pushing exoplanet RV detection limits towards Earth analogue exoplanet confirmation using the next generation of stabilised spectrographs. In this talk I will present some highlights from the HARPS-N solar telescope consortium. This telescope feeds full-disk sunlight into the HARPS-N spectrograph mounted on the Telescopio Nazionale Galileo, and thus enables observing the Sun as a star with high RV precision. In particular, I will show that the manifestations of solar activity can be tracked in individual absorption lines even on approach to the minimum of the solar cycle. Such signatures are also clearly visible in HARPS spectra of the K-dwarf alpha Cen b. For the Sun we show that plage is the main driver of these signals, not spots - but there are hints emerging in the data that suggest that more is at play here, and the detail is more complex than one might think. The ability to trace such signals in the stellar spectra may provide an important route to directly tracking the impact of stellar noise, and thus developing optimal correction techniques to yield the true stellar RVs in the future.
14:50 - 15:10 X. Dumusque: Boosting or mitigating the activity signal in radial-velocity measurements
Abstract: Stellar activity is the main limitation to the detection of Earth-twins orbiting cool stars using the radial-velocity (RV) technique, and therefore finding a way to mitigate stellar activity is crucial for a successful RV follow-up of TESS candidates. Stellar activity of quiet cool stars can be probed by looking at spectral lines presenting a chromospheric emission, like the Ca II H and K lines, H-alpha or the Ca triplet. However, spectral lines formed in the photosphere should also be affected by activity. Photospheric lines have different sensitivity to temperature, they are formed at different depth, therefore stellar activity that create spots much cooler than the photosphere and that modifies the convection as a function of depth should affect every spectral line in a different way. By deriving the RV of each individual spectral line in HARPS high-resolution spectra, we found that the RV of some spectral lines are much more sensitive to activity than others. By looking at the radial-velocity data of Alpha Centauri B in 2010 and the Sun, where clear activity signals are observed, we can either multiply by three the activity signal seen in RV, or mitigate it by a factor of 2.5, depending on the choice of lines used to measure the stellar radial velocity. By looking at the physical properties of the spectral lines used to increase or decrease the activity signal seen in RV, we are able, using machine learning algorithms, to understand what are the main physical properties of lines that make them sensitive or not to stellar activity. In conclusion, this new way of deriving RVs can be either used to probe better stellar activity, as the related signal in RV can be increased by a factor of three, or to mitigate its effects by a factor of 2.5, to detect tiny planetary signal in RV measurements.
15:10 - 15:30 M. Oshagh: Stellar activity does make exoplanets seem misaligned
Abstract: Stellar active regions, either the occulted or unocculted ones, influence the shape of high-precision transit light curves, and lead to an inaccurate estimate of the planetary parameters. Since the physics and geometry behind the transit light-curve and Rossiter-McLaughlin (RM) effect are the same, the RM observations are expected to be affected by the stellar active regions in a similar way. Oshagh et al. 2016 demonstrated, by using simulations, that inaccurate estimation on the spin-orbit angle owing to stellar activity can be significant (up to 40 degrees). Recently, we obtained high-precision RM measurements (performed by HARPS) during several transits of several exoplanets, which all transit very active stars. Our results revealed that the impact of activity on the spin-orbit angle can even be larger than the predicted values from simulation, for instance up to 60 degrees variation in the spin-orbit angle from transit to transit. Moreover, stellar activity can mimic broad band features in the transmission spectra retrieved from the chromatic RM observation.
16:00 - 16:30 S. Saar: Line Profiles, Convection, Magnetic Activity, and RVs
Abstract: It would be so much easier if stars didn't have magnetic fields... I give an overview of the many ways in which line profiles, and the radial velocities (RVs) measured from them, are affected by stellar properties, focusing in particular on those pesky magnetic fields. To reliably detect Earth-like planets, how the RVs are measured, which lines are used, the host star spectral type, magnetic activity, spatial and temporal variability are all important. I present some recent results from a combined study of SDO HMI RVs and AIA activity diagnostics for our own star to help explore these issues. The RV effects of plage, network, umbrae, penumbrae, and flares are separated and mapped out in detail. I focus on the latter two, which have been less studied to date.
16:30 - 16:50 A. Quirrenbach: Radial Velocity Measurements with m/s Precision in the Visible and Near-IR
Abstract: Precise radial velocity measurements require careful attention to detail not only in the construction of the spectrograph, but also in the calibration and data reduction procedures. While laser frequency combs provide highly stable wide-band wavelength references, the combination of hollow-cathode lamps with Fabry-Perot etalons is a cost-effective alternative. To ensure stable coupling of starlight as well as calibration light into the spectrograph, the light-scrambling properties and modal behavior of the fiber feeds must be well understood. Unexpected problems lurk in seemingly innocent active components such as steering and switching mirrors in the front end and calibration unit, as higher-order errors due to coupling between misalignments and fiber modes cannot be neglected. Detectors are never perfect, and near-infrared arrays present a set of challenges that is not encountered in CCDs, associated e.g. with cosmetic defects, electronic ghosts, and “ most insidiously “ memory effects. The latter place strong constraints on the calibration strategy, as exposing the detectors to bright lines of calibration sources shortly before taking science data must be avoided. Equal care is required in the data reduction, from processing of the raw data to extraction of the spectra, barycentric correction (requiring precise knowledge of the photon-weighted midpoint of the exposure), and computation of the radial velocity with a suitable cross-correlation technique. Compared to spectrographs working mostly in the blue, red-sensitive instruments are much more sensitive to subtleties in the treatment of telluric contamination, as non-optimal approaches can lead to systematic periodic effects on the several m/s level. We will discuss the end-to-end process of obtaining highly precise radial velocities over a wide wavelength range based on our experience with CARMENES, the first spectrograph that has been optimized for exoplanet searches in the red and near-infrared (0.52-1.72 nm).
16:50 - 17:10 M. Lafarga: Stellar activity of M dwarfs from CARMENES cross-correlation functions
Abstract: CARMENES is an instrument consisting of 2 high-resolution spectrographs designed to observe in the visible and near-infrared simultaneously. It is conducting a survey of ~300 M dwarf stars to search for planetary companions and study stellar activity. We have computed the cross-correlation functions (CCF) of the observed spectra of the CARMENES sample using different weighted binary masks. The masks were built by selecting deep and narrow absorption lines in a high signal-to-noise spectrum template obtained from coadded spectra of the CARMENES observations themselves. The resulting CCF represent a mean absorption line of the spectrum. Stellar activity deforms and changes the profile of the spectral absorption lines, which results in wavelength shifts and line asymmetries that we can measure in the CCF by means of different activity indicators. In this poster, we study the relations that exist between these activity indicators to try to understand how activity manifests in M dwarfs.
17:10 - 17:30 M. Kürster: Finding non-sinusoidal signals in time series data. Application to RV signals from planets or star spots
Absrtact: A comparative study of various periodogram techniques is presented and tested on radial velocity (RV) data of late-type stars that are either orbited by extrasolar planets or show variability due to the rotational modulation of star spots. Recently, a few new periodogram methods have been proposed, e.g. based on the Blum-Kiefer-Rosenblatt (BKR) independence test (Zucker 2016) or on the Phase Distance Correlation (PDC) approach (Zucker 2018), of which an extended (error-weighted) version is employed in this work (WPDC). These methods are capable of finding periodic signals that deviate strongly from the sinusoidal shape that is implicitely assumed by widely-used approaches such as the Generalized Lomb-Scargle (GLS) periodogram (Zechmeister & Kürster 2009) and by Fourier techniques. Especially, in cases of highly eccentric Keplerian orbits BKR and WPDC outperform GLS. At lower eccentricity WPDC and GLS are almost equally powerful. Also, for certain distributions of star spots sensitive periodogram techniques that do not require the studied signals to be close to sinusoidal are useful.
Stellar activity and RV jitter
09:00 - 09:30 A. Lanza: High-precision space borne photometry and spectral activity indicators to model activity-induced RV variations in solar-like stars
Abstract: I briefly review the mapping of photospheric active regions in solar-like stars and in the Sun based on models of their space-borne high-precision photometry. In view of the limitations of that approch to predict the activity-induced radial-velocity (RV) variations, I consider also the correlations between those RV variations and some activity indexes that can be extracted by the same spectrum used to measure the RV. Some recent results, based on the application of the kernel regression technique to a sample of slowly rotating (vsin i < 5 km/s) weakly-active (log R'HK} < -4.95) sun-like stars observed with HARPS-N are presented.
09:30 - 09:50 A. Rosich: Modeling the photosphere of active stars and the inverse problem: Starsim/2 project
Abstract: Stellar activity patterns are responsible for jitter effects observed at different timescales and amplitudes in the measurements obtained from photometric and radial velocity time series observations. These effects are usually considered just noise, and the lack of a characterization and correction strategy represents one of the main limitations to detect the signals of small exoplanets. However, this activity patterns have structure, and are not purely random noise associated to active regions (spots, faculae) but they can be modeled and studied those effects in exoplanet searches. Accurate simulations of the stellar photosphere based on the most recent available models for main sequence stars can provide synthetic photometric and spectroscopic time series data. These may help to investigate the relation between activity jitter and stellar parameters when considering different active region patterns. Moreover, jitters can be analyzed at different wavelength scales (defined by the passbands of given instruments or space missions) in order to design strategies to remove or minimize them. In this work we present the StarSim-2 tool, which is based on a model for a spotted rotating photosphere built from the integration of the spectral contribution of a fine grid of surface elements, including all significant effects affecting the flux intensities and the wavelength of spectral features produced by active regions and transiting planets. Simultaneous fits of photometry, radial velocity and activity indicators have been performed using StarSim-2, providing an approach to infer the radial velocity signal from high precision photometry and the indices derived from cross-correlation function (CCF), which are not affected by the presence of a planetary system around the star. Finally, we present an approximation to the inverse problem in stellar activity: given some observables (light curves, radial velocities, indices) we address the problem of inverting these time series to find compatible spot distributions and build probabilistic active surface maps.
09:50 - 10:10 E. Amazo Gomez: From the Sun to the Stars: Accurate rotational periods from GPS method
Abstract: Reach a clear idea of the physics involved on the activity behaviour of late-type stars is not an easy task. Even when such stars are analogs to the most analysed star, our Sun. There are many variables and degeneracies working on the whole simultaneously. Nevertheless, if there is a keystone parameter that help us to maximise the understanding of stellar dynamics, evolution, magnetic fields, chemical abundances, age, internal structure, etc., is the knowledge of the stellar rotational period. High-quality photometric data acquired from Kepler mission, high-stability and high-accuracy measurements of the solar total irradiance, TSI, from SORCE/TIM and SOHO/VIRGO missions, and detailed models of solar brightness variations allow better insights into the variability and activity of Sun-like stars. Based on the Gradient of the Power Spectra, GPS, of time series photometric data, we developed a new method to retrieve accurate values of stellar rotational periods. We present our results and a detailed characterisation of solar analogs in terms of its variability and rotation period.
10:10 - 10:30 A. Mortier: Stacking periodograms: tracking the solar rotation period and its harmonics over time
Abstract: Distinguishing between a signal induced by stellar activity or a planet is the main challenge in radial velocity (RV) searches for low-mass exoplanets these days. Even when the presence of a transiting planet and hence its period are known, stellar activity can be the main barrier in nailing down the correct amplitude of the RV signal. Observing the Sun as a star provides a unique test case to probe activity-related signals in RV data. I will present a new tool, stacking Bayesian general Lomb-Scargle periodograms, that can be used for the purpose of identifying periodicities caused by stellar activity, based on the principle that stellar activity signals are variable and incoherent over time where planet signals are not. I will show results applying this tool to three years of solar data from the HARPS-N spectrograph.
11:00 - 11:30 F. Bastien: Some new things to worry about on the path to 10cm/s
Abstract: The breadth and variety of stellar behavior unveiled in recent years, thanks in part to high precision Doppler surveys together with space-based transiting exoplanet surveys, has given us new insights into and enabled novel studies of stellar variability, stellar structure and evolution. In this talk, we present some results from our recent analysis of a large sample of stars observed with Keck HIRES as part of the California Planet Search. In particular, we highlight previously under-appreciated but relevant stellar astrophysics apparent at the few m/s level. We describe additional astrophysics observed in the Sun and in other stars that may become increasingly important as the community pushes to higher RV precision, and we suggest that broader collaboration may be key to understanding and mitigating its potential effects on precise RVs.
11:30 - 11:50 J. Jenkins: Utilising photometric activity measurements to understand the origin of newly detected small radial velocity signals
Abstract:The impact of activity on the line profiles of stellar spectra can be such that correlated noise is introduced into radial velocity measurements of even the most quiescent stars. Even more problematic can be cases where such activity features are modulated by the stellar rotation period, and have repeating patterns that can introduce Doppler-like signals into the velocity time-series, leading to the detection of false positives. Exploring ways to overcome such noise patterns, using new modelling methods and multiple data sets, can help alleviate the problem, especially if the rotational period can be pinned down. Here I will present our recent efforts to study the nearest and brightest inactive stars, using radial velocities and long-term Mt. Wilson CaII HK photometry, in order to better understand the origin of any small signals in these data. In particular, I will introduce the benefits of our new EMPEROR code, which can automatically detect very weak signals in radial velocity data, along with returning all statistically significant signals in a data set, using Bayesian model comparison methods. I will focus on our recent studies of the stars tau Ceti and, in particular, HD26965 (Diaz et al. 2018), where a small Doppler-like signal was also found to have a counterpart in Mt. Wilson chromospheric activity observations, indicating that the signal arises due to activity related noise, and not a small orbiting super-Earth. This represents an excellent example of how multiple independent data sets, both spectroscopy and photometry, can be brought together to better understand the nature of such detections. I will end discussing future lines of investigation to construct more accurate correlated noise models within the EMPEROR family of routines.
11:50 - 12:10 P. Sarkis: The case of K2-18: Cool Planets or Cool Spots?
Abstract: A major challenge for detecting low mass planets around M stars is the stellar activity. Dark spots on the surface of the star can give rise to RV variations and hence mimic the presence of a planet. Therefore, extracting weak signals in active stars is difficult, especially when the planetary orbital period is close to the stellar rotation period. K2-18 is an early M dwarf that is moderately active. I will present a combined analysis of contemporaneous photometry, multi-wavelength RV observations, and activity indicators for this system and show how such analysis can be a powerful tool to distinguish between planetary and activity signals.
12:10 - 12:30 L. Malavolta: Stellar effective temperature as a proxy for stellar activity
Absrtact: The presence of spots, plages and activity regions in general on a surface of a star will unavoidably affect its effective temperature. Using the effective temperature to track the stellar activity may seem the most logical choice, but this approach has been severely hampered by the extreme precision required to detect the small variations in temperature induced by spots and plages, which are on the order of a few Kelvin degrees or less. Encouraged by the high signal-to-noise spectra gathered with the Solar Telescope feeding the ultra-stable HARPS-N spectrograph, we explored several techniques to determine differential temperatures from massive spectroscopic datasets in an automatic fashion. In this talk I will present two methods of which preliminary results look very promising, thanks to their ability to estimate temperature with an internal precision below 1 Kelvin degree. Using these results, I'll show the connection between the RV variations induced by solar activity, chromospheric activity indexes, and the temperature of the Sun. I will then discuss the feasibility of these techniques to stars other than the Sun. The effective temperature represents a physical parameter which is straightforward to predict with respect to traditional activity indicators, and may represent the long-waited bridge between theoretical predictions and observations.
Transferring knowledge from solar to stellar observations
14:00 - 14:30 A. Shapiro: Decrypting brightness variations of Sun-like stars using solar code
Abstract: The advent of the planetary-hunting missions initiated a new era in the study of stellar photometric variabilities. We review a present state-of-the-art in the studies of stellar brightness variations and show how the solar paradigm can help us to decode them.
14:30 - 14:50 N.-E. Nemec: Solar brightness variations as they would be observed by Kepler telescope
Absrtact: Recent planet-hunting missions, such as CoRoT and Kepler opened new perspectives for studying stellar photometric variabilities on timescales of stellar rotation and below. Understanding stellar variability on such timescales, and how it compares to that of the Sun is of particular interest. While stars are observed from arbitrary directions, solar brightness variations are measured from the equatorial plane due to the special position of the Earth-bound observer. Thus, comparison studies of stars and the Sun are not straight forward and the effect of inclination has to be taking into account. Here, we model solar brightness variations on timescales of the solar rotational period and below as they would be observed out of ecliptic. For that the distribution of the magnetic features on the solar surface is calculated with the Surface Flux Transport Model developed at MPS. Using this tool allows us to disentangle two superposed effects: contributions from the rotation of the magnetic features and contributions from their evolution. We first investigate how the contribution from spots and faculae change with respect to the inclination. Next, we want to consider the combined effects of the inclination together with metallicity and effective temperature.
14:50 - 15:10 L. J. Johnson: Simulations of Stellar Variability
Abstract: Observations of rotating late-type stars reveal brightness fluctuations and periodic oscillations. This is due in part to magnetically driven activity phenomena such as cool starspots and hot faculae on the stellar surface. To facilitate analysis of this phenomenon, we present ACTReSS, a software tool for calculating the incident flux from a model active stellar surface as it varies throughout a rotation. The model uses limb-dependent intensities calculated from MURaM 3D magneto-convection simulations for quiet photospheres and magnetic active regions of varying field strength on stars of spectral type F-M. This allows us to investigate the simulated response from these features on rotational lightcurves for late-type stars with varying feature distributions and rotation axis inclinations. Simulated lightcurves are calculated at a range of inclinations for a low activity (faculae-dominated) solar analogue.
15:10 - 15:30 P. L. Palle: "Solar-SONG": A potential Helioseismology node and a versatile solar-synoptic facility. Results of the first -summer’18- campaign
Abstract: TBD
Current projects that observe the Sun as a star
16:00 - 16:30 D. Phillips: The HARPS-N Solar Telescope: Design, Testing, and Initial Results
Abstract: Detecting terrestrial exoplanets in the habitable zone of Sun-like stars requires radial velocity (RV) measurements with sensitivities well below the 1 m/s. Perturbations induced by stellar surface inhomogeneities including spots, plages and granules lead to variations in the measured stellar RV in excess of 1 m/s. Such stellar variability is difficult to study in stars other than the Sun whose surfaces are unresolved. We are therefore observing the RV of the Sun by using a small solar telescope and the HARPS-N spectrograph. This telescope, consisting of a lens feeding an integrating sphere and coupled to the HARPS-N spectrograph via an optical fiber, now operates automatically, every clear day. We characterized this telescope both in the lab and on-sky to insure: (i) sufficient scrambling by the integrating sphere; (ii) insensitivity to guiding; and (iii) consistent throughput, independent of acceptance angle such that light from the Sun fed to HARPS-N mimics the light of an unresolved star. We have observed sub-m/s sensitivity in measuring the Earth-Sun RV with this instrument. In this talk, I will present the design, demonstrations both in the lab and on-sky of its full disk RV accuracy, and a summary of the first few years of operation.
16:30 - 16:40 X. Dumusque: HELIOS
Abstract: TBD
16:40 - 16:50 A. Pevtsov: Integrated Sunlight Spectrometer (ISS) on SOLIS at NSO and Solar-Stellar Spectrograph at Lowell Observatory
Absrtact: TBD
16:50 - 17:00 S. Schäfer: Observing the Integrated and Resolved Sun with Ultra-High Spectral Resolution
Abstract: At the Institute for Astrophysics Göttingen we have a very special combination of instruments: A 50cm Siderostat with a vacuum vertical telescope, a very high resolution Fourier Transform Spectrograph (R>900,000 at 600nm in double sided mode) and a Laser Frequency Comb for extremely precise and accurate frequency calibration. The spectrograph can be fed either with the fully integrated Sun, utilizing an integrating sphere ('Sun-as-a-star') or spatially resolve the Sun (20arcsec or ~100 points along the equator). Automatic observation will allow continuous monitoring of solar features and the Sun-as-a-star.
Learning from and about solar observations
09:00 - 09:30 A. Collier Cameron: Sun-as-a-star radial velocities: navigating the hidden pitfalls
Abstract: Observing the Sun as a star with a stellar spectrograph seems straightforward enough: you feed in disc-integrated light via an optical fibre and measure the radial velocity with the same data reduction system used for stellar data. The results that emerge from this simple procedure are, however, weird. The Sun exhibits a barycentric wobble with an amplitude of 12 m/s and a period of 13 months. The radial velocity of the Sun decreases from dawn to dusk every solar day. The full width at half maximum depth of the solar cross-correlation profile oscillates with periods of 183 and 365 solar days. In this talk I discuss the causes of these odd behaviours, and present the methods I've been using to remove them from solar radial-velocity data obtained since July 2015 with the HARPS-N solar telescope.
09:30 - 10:00 A. Pevtsov: What do we learn about solar rotation and magnetic field from sun-as-a-star observations?
Abstract: TBD
10:00 - 10:20 E. Dineva: Sun-as-a-star Velocity Observations of the 2017 August 21 Solar Eclipse with PEPSI/SDI
Abstract: The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) is a state-of-the-art, thermally stabilized, fiber-fed, high-resolution spectrograph for Large Binocular Telescope (LBT) at Mt.Graham, Arizona. During day-time the instrument is fed with sunlight from the 10-millimeter aperture, fully automated, binocular Solar Disk-Integrated (SDI) telescope. The observed Sun-as-a-star spectra contain a multitude of photospheric and chromospheric spectral lines in the wavelength range of 380 - 910 nm. One of the advantages of PEPSI is that solar spectra are recorded in the exactly same manner as nighttime targets. Thus, we can compare solar and stellar spectra directly. PEPSI/SDI recorded about 100 Sun-as-a-star spectra during the 2017 August 21 solar eclipse. The observed maximum obscuration was 61.6%. We acquire consecutive data in the wavelength range of 420 - 480 nm and 530 - 630 nm with a spectral resolution R ≈ 250000 and an exposure time of 0.3s. The high-spectral resolution enables us studying subtle changes in the spectra while the Moon passes the solar disk. The Sun-as-a-star spectra are affected by changing contributions due to limb darkening and the solar differential rotation, and to a lesser extend by the presence of active regions on the solar surface. We investigate chromospheric differential rotation signatures derived from the strong Na D1 and D2 absorption lines.
10:20 - 10:40 T. Milbourne: Reproducing Measured Solar RV Variations Using Full-Disk solar Images
Abstract: On timescales of the stellar rotation period, stellar radial-velocity (RV) variations are dominated by the effects of magnetic features, such as spots and faculae. These features have velocity signatures exceeding 1 m/s, an order of magnitude larger than the 10 cm/s shift induced by an Earth-mass planet orbiting a Sun-like star. In this work, we use the Sun as a model system to study the effects of magnetic processes on measured RVs. We perform high-precision Sun-as-a-star measurements of the solar RV using a purpose-built solar telescope at HARPS-N/TNG on La Palma. RV measurements are taken near-continuously, and span three years. We compare the measured RVs with contemporaneous full-disk solar images from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) and photometry from Solar Radiation and Climate Experiment (SORCE). From this comparison, we infer the impact of magnetic features on solar convection and the solar rotation profile. We then estimate the relative contributions of these effects to the solar RVs, and investigate how these contributions vary on timescales of several rotation periods.
11:20 - 11:40 J.P. Rozelot: How big is the Sun as viewed from space? Would it be a pulsating star?
Abstract: Since the highest Antiquity we have striven to measure the sizes of celestial bodies and among them the solar diameter. Its estimate is of importance as it serves as an astronomical standard. A change in its absolute measurement may change consequently the diameter of the stars, as for all of them, they are defined relative to that of the Sun. Moreover, if the solar diameter is slowly changing with time, it may result an impact on the inferred stellar structures. How the solar shape can be seen from the far outer space? Modern 3-D solar theories show that the near sub-solar surface can be modelized and is in rather good agreement with helioseismic observations as deduced from the Solar Dynamics Observatory (SDO) NASA satellite. An aspect of this helioseismic data analysis is the accurate determination of the mode parameters particularly at high degree (i.e. â„“ up to 800), which leads to solar radius relative variations with the solar cycles modulation of amplitude. Therefore, we will show in this lecture, building on the progress made to date that our star appears from the far space as a slowly pulsating star. Such findings can be transposed to exoplanets in their environment vis-a-vis a variable host star, a fact not considered up-to-now.
11:40 - 12:00 H. Schunker: A fragile detection of g-modes in the Sun
Abstract: TBD
Frequency calibration
12:00 - 12:30 T. Steinmetz: Laser Frequency Combs for spectrograph calibration from blue to near infrared
Abstract: TBD
12:30 - 13:00 P. Huke: Calibration tools to enable high-precision RV-surveys
Abstract: In the past few years observations of the sun or sun-like stars has been done with echelle-type spectrographs orFourier Transform Spectrographs (FTS). The former are often calibrated using Fabry-Perots, gas cells, hollow-cathode lamps or Laser frequency combs (LFC). These calibrators are referenced to measurements withan FTS, which allow for a higher resolution and in principle a higher accuray. So far FTS have been calibrated successfully with few atomic lines and the wavelength solution is provided by a reference, which is often a stabilized HeNe-laser. A Laser Frequency Comb (LFC) provide a spectrum of closely spaced, narrow lines which may be better suited for characterization and calibration of an FTS. Therefore we developed a strategy to measure the spectrum of an LFC and in parallel a second sources, e.g. the sun or other calibrators. In order to make best use of the superior stability of the LFC the spectrum must be estimated properly, which enables a very high multi-spectra precision of the FTS. This strategy and an adapted setup will be used in the calibration stratgy for HIRES, the high resolution spectrograph for the ELT. We show, how we are going to achieve the challenging requirements regarding the RV-precision to fulfill HIRES science cases.
Stellar models put to the test
09:00 - 09:30 H. Cegla: Line Profile Asymmetries and Doppler Shifts: Lessons from Helioseismology and 3D Magnetohydrodynamical Solar Simulations
Abstract: Inhomogeneities on stellar surfaces pose the fundamental stumbling block on the pathway to true Earth analogues. This is especially pertinent as we enter the era of 10 cm/s radial velocity (RV) precision, with spectrographs like ESPRESSO continuing to come online. From a spectroscopic point of view, manifestations of stellar activity (such as star-spots, plage/faculae, convective flows, and oscillations) alter the observed stellar line profiles. In turn, these time-variable line asymmetries can be mistakenly interpreted as whole-sale Doppler shifts that mask or mimic planetary signals. Here, I will focus on the impact of solar surface oscillations and magnetoconvection, as these ‘noise’ sources are present on even the (magnetically) quietest exoplanet host stars. To date, the accepted approach for mitigating these noise sources is to simply try to average them out. However, this may be more appropriate for the oscillation-induced noise, and not necessarily the convection-induced signature. Using the Sun’s known power spectrum from helioseismology and applying various box-car filters, I will demonstrate that we can bin down the pressure-mode oscillations to < 10 cm/s with an exposure time of just 5.4 minutes. Moreover, I will show how exposure times slightly larger than this can actually increase the noise level, and how even doubling the exposure time has little impact. In addition, I will show how magnetoconvection does not average out well over such timescales, and how its centre-to-limb dependence can impact exoplanet measurements. Using 3D solar MHD simulations as a backbone, I will explore both the oscillation and convective induced line shape changes, and demonstrate how these changes can be used to track the remaining convective noise. Hence, in the era of 10 cm/s RV precision, I will show that we should we be fine-tuning exposure times to our host star parameters, as well as exploiting the line profile characteristics to mitigate the astrophysical noise emanating from stellar convective envelopes.
09:30 - 09:50 J. Löhner-Böttcher: High-accuracy observations of the solar atmosphere
Abstract: We performed spectroscopic high-precision observations of the Sun with the Laser Absolute Reference Spectrograph (LARS). The instrument combines the high-resolution echelle spectrograph of the German Vacuum Tower Telescope (VTT) with a laser frequency comb for absolute wavelength calibration. A careful spectral calibration yields Doppler shifts of solar spectral lines at an accuracy of a few m/s. In this talk, I will present the analysis of convective blueshifts in the quiet solar photosphere. I will demonstrate the variation of line asymmetries and absolute velocities from the disk center to the solar limb, and the change from quiet Sun to sunspot regions. For stellar or Sun-as-a-star observations, precise center-to-limb variations of convective blueshift have to be taken into account. The results presented in this talk will provide valuable input to discussions at the conference.
09:50 - 10:10 J. Maldonado: Do we really understand stellar activity? The Sun as a test case
Abstract: Understanding stellar activity in low-mass stars is crucial for the physics of stellar atmospheres as well as for ongoing exoplanet programmes. In this contribution we aim to test how well we understand stellar activity using our own star, the Sun, as a test case. We present a study of the main optical activity indicators (Ca II H & K, Balmer lines) measured in the Sun using the data provided by the solar telescope at the Telescopio Nazionale Galileo. In particular, we study their temporal evolution and correlations as well as the correlations between stellar activity and cross-correlation parameters. We finally discuss the correlations between the different activity indicators and other parameters (sunspot numbers, irradiance, ...) related to the evolution of magnetic structures in the solar atmosphere.
Disentangling spots from planets
11:00 - 11:30 S. V. Jeffers: TBD
Abstract: TBD
11:30 - 11:50 S. Sadegi: Correcting Radial Velocities for Starspot Jitter in the CARMENES Survey
Abstract:The radial velocity (RV) method is sensitive to both possible companions and activity signals arising from the host star. Activity-induced RV variations (known as RV jitter) are the ultimate obstacle for the detection of low-mass exoplanets in late-type main-sequence stars. Photospheric activity features such as cool spots and hot faculae on the stellar disc can distort the spectral line profiles and create RV jitter that may imitate or obscure the signatures of genuine planetary companions. A detailed understanding and modelling of starspot jitter is thus extremely important to avoid false-positive planet detections and erroneous estimates of the parameters of alleged planets. We are developing a novel method to disentangle starspot-induced RV jitter and true RV signals by taking advantage of the wide spectral range of CARMENES (0.52 to 0.96 µm for the visible and 0.96 to 1.71 µm for the near-infrared). This will help us to extract planetary signals in the presence of activity signals. The method exploits the fact that an RV signal induced by a planetary companion should be consistent over the whole wavelength range of the spectrograph, while spot-induced RV jitter is wavelength dependent due to the varying contrast between the hot photosphere and cool spots or even hotter faculae.
11:50 - 12:10 J. D. Alvarado Gomez: Far Beyond the Sun: Radial velocity variations over a stellar magnetic cycle
Abstract: A former member of the Hyades cluster, Horologii (Hor) is a planet-hosting Sun-like star which displays the shortest coronal activity cycle known to date (Pcyc ~ 1.6 yr). With an age of ~625 Myr, Hor is also the youngest star with a detected activity cycle. The study of its magnetic properties not only provides fundamental information on the origin of cyclic activity and stellar magnetism in late-type stars, but also serves to inform and test current efforts in correcting the effects of stellar magnetism on exoplanet radial velocity (RV) signatures. I will present the results of an ongoing long-term observing campaign aimed at studying the evolution of the magnetic cycle of Hor, using ground-based high-resolution spectropolarimetry (HARPSpol). Using the technique of Zeeman-Doppler Imaging (ZDI), we have successfully detected non-simultaneous large-scale polarity reversals associated with the azimuthal and the radial components of the magnetic field, over the course of the complex activity cycle of the star. Likewise, we unambiguously detect the expected RV signal of the ~2.5 Jupiter-mass exoplanet at approximately 310 days, regardless of the relatively large activity level variations of the star (as measured in Ca H&K S-Index or Halpha). By tracing simultaneously the evolution of the magnetic activity and the radial velocity, we find evidence of the former controlling the structure of the residual variations in the latter (once the signal from the exoplanet has been removed). While this poses a challenge in the search for additional planets in this system, a proper characterization of this behavior in light of the improvements made in the Sun-as-a-star observations, could represent a step forward in our understanding of stellar activity in the exoplanet context.
Combining techniques and data
14:00 - 14:30 E. Ford: Prospects for Modeling Stellar Spectroscopic Variability via Machine Learning
Abstract: TBD
14:30 - 14:50 N. Langellier: Estimating Radial Velocity Sensitivity of Exoplanet Detection using Gaussian Process Models of Stellar Magnetic Activity
Abstarct: The search for Earth analog exoplanets is dominated by the need to statistically capture stellar magnetic processes. Earth-mass exoplanets in the habitable zone of Sun-like stars impart tens of cm/s Doppler shifts on their host star. Magnetic features such as spots and faculae, however, can create Doppler shifts in excess of 1 m/s. These signals are modulated at the rotation period of the host star and have a typical lifetime of a few rotations. Our model of these variations is a Gaussian process (GP) with a quasi-periodic kernel function. We use the Sun as a test case, utilizing an approximately two-year series of observations of solar radial velocities from a solar telescope fed to the HARPS-N spectrograph at the TNG. We introduce radial velocity signatures of planets into both measured solar telescope radial velocities and synthesized long-baseline data sets with observing schedules and statistical properties derived from solar telescope radial velocities. We calculate detection limits for a range of masses (K = 3 m/s) and orbital periods (P = 75 days) in order to access current state of the art detection capabilities.
14:50 - 15:10 J. Faria: Realistic simulation of stellar radial velocities
Abstract: Detecting Earth-like exoplanets with the radial-velocity (RV) method is currently only possible after a successful correction of the effects of stellar activity. Since it is difficult to completely characterize the physics driving the stellar-induced signals, a number of methods have been proposed to mitigate them directly in the RV measurements. These methods, which often lack strong physical motivation, can only be tested (and improved) using either simulated datasets or those of very-well-known planetary systems. Both of these are lacking, but the latter is substantially harder to come across. In this context, I will describe an effort to create realistic simulations of RV variations induced by stellar activity, which incorporate parametrized descriptions of stellar oscillations, granulation, rotational modulation of magnetic regions, and also instrumental noise and planetary systems. These simulations, and perhaps more importantly the tool that allows to create them, have the potential to set a new standard which will help driving the development of more efficient and robust methods to disentangle stellar signals from those of Earth-like planets.
15:10 - 15:40 A. Hatzes: Towards Solar System Analogs
Abstract: One of the fundamental questions of exoplanet research is "How unique are the properties of our solar system?". Even though over 2000 exoplanetary systems have been discovered, none resemble our solar system. Thus this question is still unanswered. This is largely due to the sensitivity of the detection methods that have been employed. The transit method can detect small rocky planets, but only in short period orbits. The radial velocity (RV) method is sensitive down to icy, Neptune-like planets, but only out to orbital distances of a few AU. The detection of solar system analogs - G-type stars with rocky planets out to 2 AU, and giant planets beyond 4-5 AU - requires exquisite RV precision with a stability of 10-20 years. Complicating matters is that one most likely will have to combine data from several different instruments which may mask the detection of the smallest planets. In this talk I will discuss the prospects and limitations of detecting solar system analogs with the RV method.
The space provided for each poster is going to be A0 portrait (841 × 1189 mm), please ensure your poster fits within this area. Please check the poster's number below to find out which number your poster has been allocated.
Number #1 David Baroch Lopez: Modelling M dwarfs activity with Gaussian Processes: Hyperparameters of the CARMENES sample
Abstract: Stellar activity poses a major challenge to discover and characterize Earth-mass exoplanets. This is particularly important in the case of M-dwarf stars due to their high level of activity, although it will be crucial as well to discover Earth twins orbiting around Sun-like stars with future instruments. Several techniques have been developed to dig out exoplanet signals from stellar induced jitter either using parametric models or statistical approaches. The CARMENES project, a survey of M-dwarfs to look for Earth-like planets, is providing a large amount of spectroscopic data that can be used to study stellar activity on low-mass stars in depth. In this poster we explore Gaussian Processes as a tool to understand and model stellar activity by analysing the hyperparameters of the covariance functions used to deal with radial velocity jitter. We applied Gaussian Process techniques to a subset of the CARMENES M-dwarf sample in order to understand the physical meaning of the covariance function hyperparameters, and to study its relationship with spectral type and stellar activity spectroscopic indices. The goal is finding the most appropriate indicator to subtract the stellar radial velocity jitter for each star.
Number #2 Michael Cretignier: Mitigating activity in solar RVs using line-by-line analysis
Abstract: Stellar activity is the main obstacle to the discovery of Earth-like planets using next generation of spectrographs like ESPRESSO. However, each spectral line is affected differently by activity, due to different sensitivities to temperature and magnetic field strength. With a new reduction of solar spectra gathered by the HARPS-N solar telescope, we could analyse the RV of each individual spectral line over 120 days in 2016. This analysis allowed us to find that some lines are strongly affected by activity, while others are not. By calculating the solar RVs with unaffected lines, we can reduce the RV rms from 1.22 to 0.75 m/s, a level compatible with the HARPS-N limit of precision. The same line selection was then applied on the 1.5 years RV of the Sun showing that the long linear magnetic trend of 3.57 ± 0.20 m/s/year from the solar cycle was appreciably reduced down to 0.33 ± 0.15 m/s/year. Finally, simulations of planetary detection were performed on the 120-day data set. When using our selection of unaffected lines, detection limit is pushed from a semi-amplitude of 1 m/s down to 60 cm/s.
Number #3 Mario Damasso: Biases in retrieving planetary signals in presence of stellar activity
Abstract: Among several analysis techniques used to mitigate stellar activity signals in RV time series, Gaussian process (GP) regression is a particularly widespread tool used for detecting or characterizing exoplanets. Through extensive simulations based on a quasi-periodic representation of the stellar RV component, we have investigated our ability in retrieving planetary parameters in presence of host stars with different levels of activity. In this exploratory work, we have assumed systems with only one planet, and we have focused on the most challenging case, i.e. planets with radius less than 1.5 Re. Moreover, we have assumed orbital periods both close or well separated from the stellar rotation periods, and we have simulated RV datasets spanning up to two observing seasons, with precision typical of spectrographs like HARPS/HARPS-N or HIRES. Due to usually limited access to telescope time, target selection is a sensitive issue for every team dealing with follow-up characterization studies through spectroscopy. These simulations have been devised in particular as a tool for guiding the choice of promising targets with transiting planets discovered by space-based telescopes.
Number #4 Saeed Hojjatpanah: Selected stars for radial velocity ESPRESSO survey
Abstract: We screened the most suitable G, K and M nearby stars for the detection of Earth-class exoplanets with ESPRESSO. For most of these stars, we investigate the existence of stellar binaries. We derived the activity level using chromospheric activity indexes log(R'HK) and Ha, as well as the projected rotational velocity v sin i. For cases where planet companions are already known we also accessed the possibility that additional planets may exist in the habitable zone using dynamical arguments. We selected the best 71 stars that match our criteria for detectability of an Earth twin. The stars presented and discussed in this poster will constitute the ESPRESSO GTO catalog the RV blind search for earth-class planets. They can also be used for any other work requiring a detailed spectroscopic characterization of stars in the solar neighborhood.
Number #5 Manuel Perger:Planet detection behind strong stellar signals
Abstract: A good understanding of stellar contributions to radial velocity measurements is inevitable in order to detect low-mass planets and to fully exploit the technique's detection limits. In this poster, we present the interesting cases of two exoplanets hidden behind dominant stellar signals. Those signals show complex correlations with the stellar rotation period and its harmonics and longer-term periodicities connected to the lifetime of surface phenomena or the magnetic cycle. We explain the different methods applied to disentangle and model those different radial velocity contributions for GJ 3942 and our latest discovery.
Number #6 Lev Tal-Or: Radial-velocity variations of active stars in visual-channel CARMENES spectra
Abstract: Previous simulations predicted the activity-induced radial-velocity (RV) variations of M dwarfs to range from 1 cm/s to 1 km/s, depending on various stellar and activity parameters. We investigate the observed relations between RVs, stellar activity, and stellar parameters of M dwarfs by analyzing CARMENES high-resolution visual-channel spectra (0.5-1 µm), which were taken within the CARMENES RV planet survey during its first 20 months of operation. From each spectrum we derive a relative RV and a measure of chromospheric Halpha emission. In addition, we estimate the chromatic index (CRX) of each spectrum, which is a measure of the RV wavelength dependence. We find that the RV variations of the stars with RV scatter of >10 m/s and a projected rotation velocity vsini > 2 km/s are caused mainly by activity. We name these stars active RV-loud stars and find their occurrence to increase with spectral type: from 3% for early-type M dwarfs (M0.0, 2.5 V), through 30% for mid-type M dwarfs (M3.0, 5.5 V) to >50% for late-type M dwarfs (M6.0, 9.0 V). Their RV-scatter amplitude is found to be correlated mainly with vsini. For about half of the stars, we also find a linear RV-CRX anticorrelation, which indicates that their activity-induced RV scatter is lower at longer wavelengths. For most of the stars we can exclude a linear correlation between RV and Halpha emission. Our results are in agreement with simulated activity-induced RV variations in M dwarfs. The RV variations of most active RV-loud M dwarfs are likely to be caused by dark spots on their surfaces, which move in and out of view as the stars rotate.
Number #7 Samantha Thompson: Comparing the HARPS-N solar RVs with SORCE data: looking for improved photometric tracking of the RV variability.
Abstract: For stars of solar-like activity or quieter, faculae are likely to contribute significantly to the activity induced RV variations. Most photometric techniques for deriving RV activity signals are based on spot models and use broad visible wavebands. In this study I investigate the benefit of using different, more limited photometric wavebands to track the intrinsic activity induced RV variability of the Sun, using data from the SORCE SIM instrument and the HARPS-N solar experiment on the TNG. Since the start of the HARPS-N solar data collection ~2.5 years ago the Sun has been declining in activity, transitioning to a quieter activity phase as it approaches solar minimum (expected around 2019-2020). This is an interesting dataset to investigate how reliable different activity indicators are during the different activity cycles of the Sun and to find ones that are optimal during the phase of low activity. This will be particularly important for the Terra Hunting Experiment - our strategy is to target stars of low activity (quieter than the average Sun) so that the amplitudes of the stellar activity signals are minimised with respect to the very small planetary Doppler signal we are looking for (~10 cm/s for a planet like the Earth). However, even on a low activity star, the RV activity signal is an order of magnitude greater than that of an Earth-twin and will obscure the planetary signal. Our ability to disambiguate the effects of even low level activity thus becomes critical.
Number #8 Yvonne Unruh: Facular Contrasts on Cool Main-Sequence Stars
Abstract: Stellar variability on time scales of days and longer is predominantly driven by magnetic activity and the resulting emergence of magnetic features such as spots and faculae. We use simulations from the 3D radiation-magnetohydrodynamics code, MURaM, to represent the atmospheric structure of magnetic regions on G to M-type stars, and calculate emergent intensities from the UV (~200nm) to the far-IR (140000nm) using ATLAS9. Here we present synthetic facular contrasts for a range of cool main-sequence stars as a function of wavelength and viewing angle.
Number #9 Jesper Schou: Different Type of Spectrograph
Abstract: A persistent problem with spectrographs, especially those designed for radial velocity searches, has been to achieve the required stability. Generally the calibration has been performed by introducing a calibration signal on top of the stellar spectra, either in the form of absorption lines (e.g. using an Iodine cell) or emission lines (e.g. a ThAr lamp or a laser comb). Unfortunately these solutions have a number of problems, including removing signal, adding photon noise, unresolved lines, poor spectral coverage and cost. Here I present an outline of an alternative approach, based on techniques used in solar instrumentation, which does not add or remove any light and which provides a near perfect wavelength coverage.
Number #10 Hiroyuki Taka Ishikawa: Abundance Analysis of Mid M Dwarfs by High-Resolution Near-Infrared Spectroscopy
Abstract: Recent studies have been detecting many planets around M dwarfs. Determining the detailed chemical compositions of M dwarfs is crucial for revealing the formation processes of the planetary systems and constraining the internal structures of the terrestrial planets around them. However, their intrinsic faintness and dominant molecular absorption hinder the well-established measurements of accurate chemical composition with high-resolution optical spectra. The problems are mitigated in near-infrared wavelength. IRD is such a high-resolution near-infrared spectrometer for the Subaru Telescope constructed for a planet search around nearby M dwarfs. IRD is the first instrument for 8m-class telescopes to cover the Y, J, and H bands simultaneously with a maximum spectral resolution of 70,000. The large diameter and broadband coverage have made it possible to observe more atomic lines than ever before in near-IR spectra of faint M dwarfs. We verified that the quality of IRD spectra is comparable to the existing ones such as CRIRES spectra in terms of wavelength assignment and resolution. We report the chemical abundance analysis of IRD spectra of Barnard’s Star. We identified the absorption lines throughout the Y, J, and H bands. We determined the elemental abundances for Fe, Ti, Cr, Na, Mg, Al, Si, K, Ca, V, and Mn, based on the equivalent width of the corresponding atomic lines. We also detected more than 100 FeH lines, which are dominant in Y band, and examined their behavior.
Number #11 Mathias Zechmeister: The color of RVs: Observing the wavelength dependency of spots with CARMENES
Abstract: Spots distort atomic and molecular lines of the stellar quiet photosphere due to temperature contrast. They can shift the apparent line centers in the spectrum of an active star. The generated Doppler velocities depend on wavelength because the contrast between spot and photosphere does so. The CARMENES spectrograph simultaneously covers the wavelength range 520-1710nm. In our M dwarf survey, we observed several active stars with significant RV excursions. We analyze the wavelength dependent signature of starspots and find that active stars can behave very differently. The color of RVs adds a new dimension to the analysis of Doppler velocities providing a fresh view into the properties of active stars.
Number #12 Sourav Palit: Estimation of surface radiation environment in terrestrial exoplanets and it's influence on early biology and habitability
Abstract: The radiation environment on terrestrial exoplanets and it's probable influence on the early biological evolution and habitability can be studied on the basis of the knowledge acquired on the solar irradiation on the planets of our solar system and how it changes over time depending on solar and planetary atmospheric evolution. Similar to the sun, the UV and X-ray radiation from exoplanet's host stars, in various stages of their life should have varying influence on the planetary biology. The atmospheric conditions of planets such as carbon dioxide reservoir, abundance of ozone (or other greenhouse gases), presence of haze and cloud etc., which determine the penetration of such radiation in the atmosphere should also play a decisive role. Stellar energetic particles may also have significance direct and indirect influence by modulating cosmic ray incident fluxes, which also depends on the type of planetary magnetic protection, if there is any and on the stellar activity levels. We have developed a Monte Carlo radiative transfer code to accommodate various possible exoplanet atmospheres and stellar conditions using the current understanding of the radiation environment of solar system planets and it's evolution. Surface radiation environments calculated for few terrestrial exoplanets, as test cases are employed to estimate the effects on biology in terms of the modification of carbon cycle and methane production with the interaction of meteoritic in-fall, photobiological response of the DNA, possible photolysis and overall effect on water and soil chemistry etc. In the course of the study we also gain some valuable inference on the possible biosignature detectability.
Number #13 Sebastian Schäfer: Observing the Integrated and Resolved Sun with Ultra-High Spectral Resolution
Abstract: At the Institute for Astrophysics Göttingen we have a very special combination of instruments: A 50cm Siderostat with a vacuum vertical telescope, a very high resolution Fourier Transform Spectrograph (R>900,000 at 600nm in double sided mode) and a Laser Frequency Comb for extremely precise and accurate frequency calibration. The spectrograph can be fed either with the fully integrated Sun, utilizing an integrating sphere ('Sun-as-a-star') or spatially resolve the Sun (20arcsec or ~100 points along the equator). Automatic observation will allow continuous monitoring of solar features and the Sun-as-a-star.
Number #14 Diana Kossakowski: Enigmatic AD Leo: Starspot, Planet, or Both?
Abstract: If our goal is to detect exoplanets, the amplitude of a periodic signal present in Radial Velocity (RV) data should be both time- and wavelength-independent. However, an on-going issue present is our limitation in both time and wavelength space. Essentially, we are not getting the full picture, and stellar activity, especially in M dwarfs, can mimic a planetary signal if a given time-wavelength subspace is not adequate enough. In an attempt to address the wavelength coverage, the instrument CARMENES consists of two separate high-resolution echelle spectrographs, covering the VIS and NIR wavelengths from 520-960 nm and 960-1710 nm, respectively. Therefore, it can aid in determining whether a signal is truly due to a planetary companion or due to activity in the star itself. An additional tool is to look at the ChRomatic IndeX (CRX), where a correlation between the RV and the CRX indicates stellar activity due to the temperature difference between a spot and the star’s quiescent photosphere. A stellar target proved to be interesting to study is AD Leo, a M3 dwarf known to be highly active. The literature reports a 23 m/s signal with a period around 2.23 days using HARPS, whose wavelength range is 383-690 nm, and therefore bluer than CARMENES. The amplitude of the signal was claimed to be relatively constant throughout the HARPS wavelength regime, and therefore, a CARMENES campaign for AD Leo was carried out to investigate the wavelength-dependency of the signal. The CARMENES data in the VIS shows the periodicity of 2.23 days with a similar semi-amplitude and phase, even though it is taken 10 years after the HARPS data, which could be consistent with a planetary signal. However, when considering both the VIS and NIR, it is found that the amplitude of this signal is decreasing with wavelength at first, but then plateaus off in the longer wavelength regime. Here, I present RV data that extends all the way to the NIR as well as a discussion considering possible explanations as to why this 2.23 day periodic signal of a highly active early M dwarf star behaves in such a manner.
Number #15 David Phillips: Astro-comb Wavelength Calibrator for HARPS-N
Abstract: Detecting terrestrial exoplanets in the habitable zone of Sun-like stars requires radial velocity measurements with sensitivities well below the 1 m/s. One element that will be crucial to such sensitivity is stable long-term wavelength calibration. The next generation of ultra-stable wavelength calibrators is based on laser frequency combs: pulsed lasers producing a series of calibration lines at evenly spaced optical frequencies whose exact wavelengths can be derived by radio frequency measurements compared to atomic clocks and the Global Positioning System (GPS). At the TNG/HARPS-N we are deploying a visible wavelength laser frequency comb as a wavelength calibration source. Our calibrator, known as an astro-comb, is realized by spectrally broadening and shifting the output of a 1 GHz repetition rate modelocked Ti:sapphire laser using a photonic crystal fiber and then filtering the comb lines to create a coarse-toothed comb with 16 GHz line spacing. Results, including stability and instrument profile measurements, from the first generation astro-comb will be presented along with the status of the fully automated comb currently being implemented at the TNG.
Number #16 Nick Langellier: Estimating Radial Velocity Sensitivity of Exoplanet Detection using Gaussian Process Models of Stellar Magnetic Activity
Abstract: The search for Earth analog exoplanets is dominated by the need to statistically capture stellar magnetic processes. Earth-mass exoplanets in the habitable zone of Sun-like stars impart tens of cm/s Doppler shifts on their host star. Magnetic features such as spots and faculae, however, can create Doppler shifts in excess of 1 m/s. These signals are modulated at the rotation period of the host star and have a typical lifetime of a few rotations. Our model of these variations is a Gaussian process (GP) with a quasi-periodic kernel function. We use the Sun as a test case, utilizing an approximately two-year series of observations of solar radial velocities from a solar telescope fed to the HARPS-N spectrograph at the TNG. We introduce radial velocity signatures of planets into both measured solar telescope radial velocities and synthesized long-baseline data sets with observing schedules and statistical properties derived from solar telescope radial velocities. We calculate detection limits for a range of masses (K = 3 m/s) and orbital periods (P = 75 days) in order to access current state of the art detection capabilities.
Number #17 Tim Milbourne: The Sun as a Model for Stellar Activity
Abstract: To detect Earth-like exoplanets in the habitable zones of Sun-like stars, Precise Radial Velocity spectrographs require sensitivities below 10 cm/s. To realize these design goals, non-planetary variability in the measured radial velocity (RV) must be understood and its effects accounted for. On timescales of the stellar rotation period, these non-planetary RV variations are dominated by the effects of magnetic features, such as spots and faculae, which have velocity signatures exceeding 1 m/s. In this work, we use the Sun as a model system for the effects of magnetic processes on RV measurements. We perform high-precision Sun-as-a-star measurements of the solar RV using a purpose-built solar telescope and the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph on La Palma. In parallel, we use magnetograms from the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory and simultaneous photometry from Solar Radiation and Climate Experiment to extract information about how magnetic features interact with solar convection and change the solar rotation profile, and how these effects change the solar RVs. By combining these data sources, we estimate the relative contributions of solar magnetic variations to the solar RVs, and investigate how these contributions vary with time.
Number #18 Steven H. Saar: A First Look At the Effect of Flares on Radial Velocity Jitter in G Dwarfs: A Punch and a Splash?
Abstract: We make an initial study of the radial velocity (RV) effects of flares in solar-like stars by turning to the nearest one: our Sun! This is part of a broader study of the RV effects of different magnetic region types using our own G2 star. We use SDO HMI to obtain radial velocities and AIA to collect FUV images (170 nm) across the solar disk every 4 hours throughout 2014, near a peak of the latest magnetic cycle. We use the 170 nm images to identify plage, network, and (apparent) flares. We find that flares are more strongly redshifted near disk center, and strongly blueshifted towards the limb. We interpret this as observing the flare impact (the "punch") in the chromosphere, compressing material away from the viewer, near disk center, and the horizontal "splash" or expansion due to that impact towards the limb. Flare pixels show the largest scatter of any magnetic feature at fixed mu, consistent with seeing a variety of unevenly sampled events of different energy. The flare RV(mu) curve is distinct from all other magnetic features and thus likely captures a distinct (flare) phemonenon. However the distribution of flaring pixels N_flare(mu). shows an unexpected peak at disk center -- there were almost no disk-center flares seen by the GOES satellite in 2014. We develop a plausible model for the N_flare distribution, and suggest a solution to this mystery.