Spatially resolved spectroscopy across stellar surfaces

Dravins, Dainis; Ludwig, H.‐G.; Freytag, B.

doi:10.1051/0004-6361/202039997

Cited by 16 publications

(13 citation statements)

References 150 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In spectroscopic observations, granulation produces shifts and asymmetries in the spectral lines (i.e., the line bisectors, see Dravins et al 1981;Nordlund 1985;Dravins 1987;Asplund et al 2000;Asplund et al 2000;Gray 2009;Nordlund et al 2009;Dravins et al 2021). Studying RV time series of a small sample of main-sequence and subgiant stars, Bastien et al (2014) found a correlation between the RV root-mean-square (RMS) evolving on timescales shorter than 8 hours (or the "8hour RV scatter") and the stellar surface gravity.…”

Section: Introductionmentioning

confidence: 99%

Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO

Sulis¹,

Lendl²,

Cegla³

et al. 2023

A&A

View full text Add to dashboard Cite

Context. Stellar granulation generates fluctuations in photometric and spectroscopic data whose properties depend on the stellar type, composition, and evolutionary state. Characterizing granulation is key for understanding stellar atmospheres and detecting planets. Aims. We aim to detect the signatures of stellar granulation, link spectroscopic and photometric signatures of convection for main-sequence stars, and test predictions from 3D hydrodynamic models. Methods. For the first time, we observed two bright stars (T eff = 5833 K and 6205 K) with high-precision observations taken simultaneously with CHEOPS and ESPRESSO. We analyzed the properties of the stellar granulation signal in each individual dataset. We compared them to Kepler observations and 3D hydrodynamic models. While isolating the granulation-induced changes by attenuating and filtering the p-mode oscillation signals, we studied the relationship between photometric and spectroscopic observables.Results. The signature of stellar granulation is detected and precisely characterized for the hotter F star in the CHEOPS and ESPRESSO observations. For the cooler G star, we obtain a clear detection in the CHEOPS dataset only. The TESS observations are blind to this stellar signal. Based on CHEOPS observations, we show that the inferred properties of stellar granulation are in agreement with both Kepler observations and hydrodynamic models. Comparing their periodograms, we observe a strong link between spectroscopic and photometric observables. Correlations of this stellar signal in the time domain (flux versus radial velocities, RV) and with specific spectroscopic observables (shape of the cross-correlation functions) are however difficult to isolate due to S/N dependent variations. Conclusions. In the context of the upcoming PLATO mission and the extreme precision RV surveys, a thorough understanding of the properties of the stellar granulation signal is needed. The CHEOPS and ESPRESSO observations pave the way for detailed analyses of this stellar process.

show abstract

Section: Introductionmentioning

confidence: 99%

Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO

Sulis¹,

Lendl²,

Cegla³

et al. 2023

A&A

View full text Add to dashboard Cite

show abstract

“…Salient features of line profiles include how their widths, depths, and wavelength positions change across stellar surfaces. As we will explore in Paper V (Dravins et al 2021), these are the parameters that are least challenging to observe, also remaining distinguishable in noisier data at the lower resolutions of current spectrometers. 4.5 hyd0007 -'K8 Notes.…”

Section: Outlook and Outstanding Issuesmentioning

confidence: 99%

“…Anticipating such observations, this Paper IV surveys complete synthetic spectra for stars of different temperatures to identify patterns that are unique for 3D models and plausible to identify in realistically complex spectra with a multitude of often overlapping or blending lines. The following Paper V (Dravins et al 2021) evaluates which spectral features should be practically observable, depending on the signal-to-noise and spectral resolution that can be attained.…”

Section: Spectra From 3d Hydrodynamic Atmospheresmentioning

confidence: 99%

“…This Paper IV explores observable spectral-line shapes and shifts, in the range 400-700 nm, from complete synthetic spectra of different spectral types obtained from hydrodynamic 3D simulations. The subsequent Paper V (Dravins et al 2021) will examine the practical observability of specific spectral features (and their variability in time) when observed with realistic instrumentation.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Spatially resolved spectroscopy across stellar surfaces

Dravins

Ludwig

Freytag

2021

A&A

Self Cite

View full text Add to dashboard Cite

Context. High-precision stellar analyses require hydrodynamic 3D modeling. Such models predict changes across stellar disks of spectral line shapes, asymmetries, and wavelength shifts. For testing models in stars other than the Sun, spatially resolved observations are feasible from differential spectroscopy during exoplanet transits, retrieving spectra of those stellar surface segments that successively become hidden behind the transiting planet, as demonstrated in Papers I, II, and III. Aims. Synthetic high-resolution spectra over extended spectral regions are now available from 3D models. Similar to other ab initio simulations in astrophysics, these data contain patterns that have not been specifically modeled but may be revealed after analyses to be analogous to those of a large volume of observations. Methods. From five 3D models spanning Teff = 3964–6726 K (spectral types ~K8 V–F3 V), synthetic spectra at hyper-high resolution (λ/Δλ >1 000 000) were analyzed. Selected Fe I and Fe II lines at various positions across stellar disks were searched for characteristic patterns between different types of lines in the same star and for similar lines between different stars. Results. Spectral-line patterns are identified for representative photospheric lines of different strengths, excitation potentials, and ionization levels, thereby encoding the hydrodynamic 3D structure. Line profiles and bisectors are shown for various stars at different positions across stellar disks. Absolute convective wavelength shifts are obtained as differences to 1D models, where such shifts do not occur. Conclusions. Observable relationships for line properties are retrieved from realistically complex synthetic spectra. Such patterns may also test very detailed 3D modeling, including non-LTE effects. While present results are obtained at hyper-high spectral resolution, the subsequent Paper V examines their practical observability at realistically lower resolutions, and in the presence of noise.

show abstract

“…So far, only ESPRESSO (Pepe et al 2021) is capable of doing this task and it will still be challenging for this ultra-stable instrument. Solar-like stars also have higher granulation levels and noise, thus increasing the stellar jitter (see, e.g., Dumusque et al 2011;Cegla 2019;Dravins et al 2021).…”

Section: Introductionmentioning

confidence: 99%

The KOBE experiment: K-dwarfs Orbited By habitable Exoplanets

Lillo-Box

Santos

Santerne

et al. 2022

A&A

View full text Add to dashboard Cite

The detection of habitable worlds is one of humanity's greatest endeavors. Thus far, astrobiological studies have shown that one of the most critical components for allowing life to develop is liquid water. Its chemical properties and its capacity to dissolve and, hence, transport other substances makes this constituent a key piece in this regard. As a consequence, looking for life as we know it is directly related to the search for liquid water. For a remote detection of life in distant planetary systems, this essentially means looking for planets in the so-called habitable zone. In this sense, K-dwarf stars are the perfect hosts to search for planets in this range of distances. Contrary to G-dwarfs, the habitable zone is closer, thus making planet detection easier using transit or radial velocity techniques. Contrary to M-dwarfs, stellar activity is on a much smaller scale, hence, it has a smaller impact in terms of both the detectability and the true habitability of the planet. Also, K-dwarfs are the quietest in terms of oscillations, and granulation noise. In spite of this, there is a dearth of planets in the habitable zone of K-dwarfs due to a lack of observing programs devoted to this parameter space. In response to a call for legacy programs of the Calar Alto observatory, we have initiated the first dedicated and systematic search for habitable planets around these stars: K-dwarfs Orbited By habitable Exoplanets (KOBE). This survey is monitoring the radial velocity of 50 carefully pre-selected K-dwarfs with the CARMENES instrument over five semesters, with an average of 90 data points per target. Based on planet occurrence rates convolved with our detectability limits, we expect to find 1.68 ± 0.25 planets per star in the KOBE sample. Furthermore, in half of the sample, we expect to find one of those planets within the habitable zone. Here, we describe the motivations, goals, and target selection for the project as well as the preliminary stellar characterization.

show abstract

Spatially resolved spectroscopy across stellar surfaces

Cited by 16 publications

References 150 publications

Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO

Connecting photometric and spectroscopic granulation signals with CHEOPS and ESPRESSO

Spatially resolved spectroscopy across stellar surfaces

The KOBE experiment: K-dwarfs Orbited By habitable Exoplanets

Contact Info

Product

Resources

About