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311. Carbon depletion observed inside T Tauri inner rims
ID:
ivo://CDS.VizieR/J/A+A/632/A32
Title:
Carbon depletion observed inside T Tauri inner rims
Short Name:
J/A+A/632/A32
Date:
21 Oct 2021
Publisher:
CDS
Description:
The carbon content of protoplanetary disks is an important parameter to characterize planets formed at different disk radii. There is some evidence from far-infrared and submillimeter observations that gas in the outer disk is depleted in carbon, with a corresponding enhancement of carbon-rich ices at the disk midplane. Observations of the carbon content inside of the inner sublimation rim could confirm how much cpc on remains locked in kilometer size bodies in the disk. I aim to determine the density, temperature, and carbon abundance inside the disk dust sublimation rim in a set of T Tauri stars with full protoplanetary disks. Using medium-resolution, near-infrared (0.8 to 2.5um) spectra and the new GAIA DR2 distances, I self-consistently determine the stellar, extinction, veiling, and accretion properties of the 26 stars in my sample. From these values, and non-accreting T Tauri spectral templates, I extract the inner disk excess of the target stars from their observed spectra. Then I identify a series of C0 recombination lines in 18 of these disks and use the CHIANTI atomic line database with an optically thin slab model to constrain the average ne, Te, and nC for these lines in the five disks with a complete set of lines. By comparing these values with other slab models of the inner disk using the Cloudy photoionization code, I also constrain nH and the carbon abundance, XC, and hence the amount of carbon 'missing' from the slab. For one disk, DR Tau, I use relative abundances for the accretion stream from the literature to also determine XSi and XN . The inner disks modeled here are extremely dense (nH~10^16^cm^-3^), warm (Te~4500K), and moderately ionized (logXe~3.3). Three of the five modeled disks show robust carbon depletion up to a factor of 42 relative to the solar value. I discuss multiple ways in which the 'missing' carbon could be locked out of the accreting gas. Given the high-density inner disk gas, evidence for radial drift, and lack of obvious gaps in these three systems, their carbon depletion is most consistent with the 'missing' carbon being sequestered in kilometer size bodies. For DR Tau, nitrogen and silicon are also depleted by factors of 45 and 4, respectively, suggesting that the kilometer size bodies into which the grains are locked were formed beyond the N_2_ snowline. I explore briefly what improvements in the models and observations are needed to better address this topic in the future.
312. Carbon-enhanced metal-poor star BD+44493 EWs
ID:
ivo://CDS.VizieR/J/ApJ/824/L19
Title:
Carbon-enhanced metal-poor star BD+44493 EWs
Short Name:
J/ApJ/824/L19
Date:
21 Oct 2021
Publisher:
CDS
Description:
The carbon-enhanced metal-poor star BD+44{deg}493 ([Fe/H]=-3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope. We derive [P/Fe]=-0.34+/-0.21, [S/Fe]=+0.07+/-0.41, and [Zn/Fe]=-0.10+/-0.24. We increase by 10-fold the number of SiI lines detected in BD+44493, yielding [Si/Fe]=+0.15+/-0.22. The [S/Fe] and [Zn/Fe] ratios exclude the hypothesis that the abundance pattern in BD+44493 results from depletion of refractory elements onto dust grains. Comparison with zero-metallicity supernova (SN) models suggests that the stellar progenitor that enriched BD+44493 was massive and ejected much less than 0.07M_{sun}_ of ^56^Ni, characteristic of a faint SN.
313. Carbon in red giants in GCs and dSph galaxies
ID:
ivo://CDS.VizieR/J/ApJ/801/125
Title:
Carbon in red giants in GCs and dSph galaxies
Short Name:
J/ApJ/801/125
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present carbon abundances of red giants in Milky Way (MW) globular clusters and dwarf spheroidal galaxies (dSphs). Our sample includes measurements of carbon abundances for 154 giants in the clusters NGC2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax, Ursa Minor, and Draco. This sample doubles the number of dSph stars with measurements of [C/Fe]. The [C/Fe] ratio in the clusters decreases with increasing luminosity above (L/L_{sun}_)~=1.6, which can be explained by deep mixing in evolved giants. The same decrease is observed in dSphs, but the initial [C/Fe] of the dSph giants is not uniform. Stars in dSphs at lower metallicities have larger [C/Fe] ratios. We hypothesize that [C/Fe] (corrected to the initial carbon abundance) declines with increasing [Fe/H] due to the metallicity dependence of the carbon yield of asymptotic giant branch stars and due to the increasing importance of SNe Ia at higher metallicities. We also identified 11 very carbon-rich giants (eight previously known) in three dSphs. However, our selection biases preclude a detailed comparison to the carbon-enhanced fraction of the MW stellar halo. Nonetheless, the stars with [C/Fe]<+1 in dSphs follow a different [C/Fe] track with [Fe/H] than the halo stars. Specifically, [C/Fe] in dSphs begins to decline at lower [Fe/H] than in the halo. The difference in the metallicity of the [C/Fe] "knee" adds to the evidence from [{alpha}/Fe] distributions that the progenitors of the halo had a shorter timescale for chemical enrichment than the surviving dSphs.
314. Carbon stars from LAMOST DR2 data
ID:
ivo://CDS.VizieR/J/ApJS/226/1
Title:
Carbon stars from LAMOST DR2 data
Short Name:
J/ApJS/226/1
Date:
21 Oct 2021
Publisher:
CDS
Description:
In this work, we present the new catalog of carbon stars from the LAMOST DR2 catalog. In total, 894 carbon stars are identified from multiple line indices measured from the stellar spectra. We are able to identify the carbon stars by combining the CN bands in the red end with C_2_ and other lines. Moreover, we also classify the carbon stars into spectral sub-types of C-H, C-R, and C-N. These sub-types show distinct features in the multi-dimensional line indices, implying that in the future they can be used to identify carbon stars from larger spectroscopic data sets. While the C-N stars are clearly separated from the others in the line index space, we find no clear separation between the C-R and C-H sub-types. The C-R and C-H stars seem to smoothly transition from one to another. This may hint that the C-R and C-H stars may not be different in their origins, instead their spectra look different because of different metallicities. Due to the relatively low spectral resolution and lower signal-to-noise ratio, the ratio of ^12^C/^13^C is not measured and thus the C-J stars are not identified.
315. Carbon stars spectra and photometry values
ID:
ivo://CDS.VizieR/J/A+A/589/A36
Title:
Carbon stars spectra and photometry values
Short Name:
J/A+A/589/A36
Date:
21 Oct 2021
Publisher:
CDS
Description:
We provide a new collection of spectra of 35 carbon stars obtained with the ESO/VLT X-shooter instrument as part of the X-shooter Spectral Library project. The spectra extend from 0.3um to 2.4um with a resolving power above ~8000. The sample contains stars with a broad range of (J-K) color and pulsation properties located in the Milky Way and the Magellanic Clouds. We show that the distribution of spectral properties of carbon stars at a given (J-K) color becomes bimodal (in our sample) when (J-K) is larger than about 1.5. We describe the two families of spectra that emerge, characterized by the presence or absence of the absorption feature at 1.53um, generally associated with HCN and C_2_H_2_. This feature appears essentially only in large-amplitude variables, though not in all observations. Associated spectral signatures that we interpret as the result of veiling by circumstellar matter, indicate that the 1.53um feature might point to episodes of dust production in carbon-rich Miras.
316. CARMENES input catalogue of M dwarfs. I
ID:
ivo://CDS.VizieR/J/A+A/577/A128
Title:
CARMENES input catalogue of M dwarfs. I
Short Name:
J/A+A/577/A128
Date:
21 Oct 2021
Publisher:
CDS
Description:
CARMENES is a stabilised, high-resolution, double-channel spectrograph at the 3.5m Calar Alto telescope. It is optimally designed for radial-velocity surveys of M dwarfs with potentially habitable Earth-mass planets. We prepare a list of the brightest, single M dwarfs in each spectral subtype observable from the northern hemisphere, from which we will select the best planet-hunting targets for CARMENES. In this first paper on the preparation of our input catalogue, we compiled a large amount of public data and collected low-resolution optical spectroscopy with CAFOS at the 2.2m Calar Alto telescope for 753 stars. We derived accurate spectral types using a dense grid of standard stars, a double least-squares minimisation technique, and 31 spectral indices previously defined by other authors. Additionally, we quantified surface gravity, metallicity, and chromospheric activity for all the stars in our sample. We calculated spectral types for all 753 stars, of which 305 are new and 448 are revised. We measured pseudo-equivalent widths of H{alpha} for all the stars in our sample, concluded that chromospheric activity does not affect spectral typing from our indices, and tabulated 49 stars that had been reported to be young stars in open clusters, moving groups, and stellar associations. Of the 753 stars, two are new subdwarf candidates, three are T Tauri stars, 25 are giants, 44 are K dwarfs, and 679 are M dwarfs. Many of the 261 investigated dwarfs in the range M4.0-8.0 V are among the brightest stars known in their spectral subtype.
317. CARMENES obs. of the binary system LB-1
ID:
ivo://CDS.VizieR/J/ApJ/900/42
Title:
CARMENES obs. of the binary system LB-1
Short Name:
J/ApJ/900/42
Date:
21 Mar 2022 09:26:37
Publisher:
CDS
Description:
The mass, origin, and evolutionary stage of the binary system LB-1 have been intensely debated, following the claim that it hosts an ~70M_{sun}_ black hole, in stark contrast with the expectations for Galactic remnants. We conducted a high-resolution, phase-resolved spectroscopic study of its Paschen lines, using the Calar Alto 3.5m telescope. We find that Pa{beta} and Pa{gamma} (after subtraction of the stellar absorption component) are well fitted with a standard double-peaked disk profile. We measured the velocity shifts of the red and blue peaks at 28 orbital phases: the line center has an orbital motion in perfect antiphase with the secondary, and the radial velocity amplitude ranges from 8 to 13km/s, for different methods of profile modeling. We interpret this curve as proof that the disk traces the orbital motion of the primary, ruling out the circumbinary disk and the hierarchical triple scenarios. The phase-averaged peak-to-peak half-separation (a proxy for the projected rotational velocity of the outer part of the disk) is ~70km/s, larger than the orbital velocity of the secondary and inconsistent with a circumbinary disk. From those results, we infer a primary mass 4-8 times higher than the secondary mass. Moreover, we show that the intensity ratio of the blue and red peaks has a sinusoidal behavior in phase with the secondary, which we attribute to external irradiation of the outer part of the disk. Finally, we discuss our findings in the context of competing scenarios proposed for LB-1. Further astrometric Gaia data will test between alternative solutions.
318. CARMENES stars multi wavelength measurements
ID:
ivo://CDS.VizieR/J/A+A/627/A161
Title:
CARMENES stars multi wavelength measurements
Short Name:
J/A+A/627/A161
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present precise photospheric parameters of 282 M dwarfs determined from fitting the most recent version of PHOENIX models to high-resolution CARMENES spectra in the visible (0.52-0.96um) and near-infrared wavelength range (0.96-1.71um). With its aim to search for habitable planets around M dwarfs, several planets of different masses have been detected. The characterization of the target sample is important for the ability to derive and constrain the physical properties of any planetary systems that are detected. As a continuation of previous work in this context, we derived the fundamental stellar parameters effective temperature, surface gravity, and metallicity of the CARMENES M-dwarf targets from PHOENIX model fits using a {chi}^2^ method. We calculated updated PHOENIX stellar atmosphere models that include a new equation of state to especially account for spectral features of low-temperature stellar atmospheres as well as new atomic and molecular line lists. We show the importance of selecting magnetically insensitive lines for fitting to avoid effects of stellar activity in the line profiles. For the first time, we directly compare stellar parameters derived from multi wavelength range spectra, simultaneously observed for the same star. In comparison with literature values we show that fundamental parameters derived from visible spectra and visible and near-infrared spectra combined are in better agreement than those derived from the same spectra in the near-infrared alone.
319. CARMENES stellar atmospheric parameters
ID:
ivo://CDS.VizieR/J/A+A/656/A162
Title:
CARMENES stellar atmospheric parameters
Short Name:
J/A+A/656/A162
Date:
22 Feb 2022
Publisher:
CDS
Description:
We determine effective temperatures, surface gravities, and metallicities for a sample of 343 M dwarfs observed with CARMENES, the double-channel, high-resolution spectrograph installed at the 3.5m telescope at Calar Alto Observatory. We employed SteParSyn, a Bayesian spectral synthesis implementation, along with a grid of synthetic spectra based on BT-Settl model atmospheres and the radiative transfer code turbospectrum. The synthetic grid was computed around 75 magnetically insensitive TiI and FeI along with the TiO gamma- and epsilon-bands. To avoid degeneracies in the parameter space, we imposed Bayesian priors based on multi-band photometric data available for the sample.
320. CARMENES time-resolved CaII H&K catalog
ID:
ivo://CDS.VizieR/J/A+A/652/A116
Title:
CARMENES time-resolved CaII H&K catalog
Short Name:
J/A+A/652/A116
Date:
22 Feb 2022
Publisher:
CDS
Description:
Radial-velocity (RV) jitter caused by stellar magnetic activity is an important factor in state-of-the-art exoplanet discovery surveys such as CARMENES. Stellar rotation, along with heterogeneities in the photosphere and chromosphere caused by activity, can result in false-positive planet detections. Hence, it is necessary to determine the stellar rotation period and compare it to any putative planetary RV signature. Long-term measurements of activity indicators such as the chromospheric emission in the CaII H&K lines enable the identification of magnetic activity cycles. In order to determine stellar rotation periods and study the long-term behavior of magnetic activity of the CARMENES guaranteed time observations (GTO) sample, it is advantageous to extract R'HK time series from archival data, since the CARMENES spectrograph does not cover the blue range of the stellar spectrum containing the Ca II H&K lines. We have assembled a catalog of 11634 archival spectra of 186 M dwarfs acquired by seven different instruments covering the CaII H&K regime: ESPADONS, FEROS, HARPS, HIRES, NARVAL, TIGRE, and UVES. The relative chromospheric flux in these lines, R'HK, was directly extracted from the spectra by rectification with PHOENIX synthetic spectra via narrow passbands around the Ca II H&K line cores. The combination of archival spectra from various instruments results in time series for 186 stars from the CARMENES GTO sample. As an example of the use of the catalog, we report the tentative discovery of three previously unknown activity cycles of M dwarfs. We conclude that the method of extracting R'HK with the use of model spectra yields consistent results for different instruments and that the compilation of this catalog will enable the analysis of long-term activity time series for a large number of M dwarfs.

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