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101. High-resolution spectroscopy of TESS stars
ID:
ivo://CDS.VizieR/J/ApJS/248/19
Title:
High-resolution spectroscopy of TESS stars
Short Name:
J/ApJS/248/19
Date:
21 Oct 2021
Publisher:
CDS
Description:
Accurate atmospheric parameters and chemical composition of stars play a vital role in characterizing physical parameters of exoplanetary systems and understanding of their formation. A full asteroseismic characterization of a star is also possible if its main atmospheric parameters are known. The NASA Transiting Exoplanet Survey Satellite (TESS) space telescope will play a very important role in searching of exoplanets around bright stars and stellar asteroseismic variability research. We have observed all 302 bright (V<8mag) and cooler than F5 spectral class stars in the northern TESS continuous viewing zone with a 1.65m telescope at the Moletai Astronomical Observatory of Vilnius University and the high-resolution Vilnius University Echelle Spectrograph. We uniformly determined the main atmospheric parameters, ages, orbital parameters, velocity components, and precise abundances of 24 chemical species (C(C2), N(CN), [OI], NaI, MgI, AlI, SiI, SiII, CaI, CaII, ScI, ScII, TiI, TiII, VI, CrI, CrII, MnI, FeI, FeII, CoI, NiI, CuI, and ZnI) for 277 slowly rotating single stars in the field. About 83% of the sample stars exhibit the Mg/Si ratios greater than 1.0 and may potentially harbor rocky planets in their systems.
102. High-res. spectroscopy of LAMOST Li-rich giants
ID:
ivo://CDS.VizieR/J/ApJ/877/104
Title:
High-res. spectroscopy of LAMOST Li-rich giants
Short Name:
J/ApJ/877/104
Date:
21 Oct 2021
Publisher:
CDS
Description:
The discovery of Li-rich giants has introduced a new challenge for standard stellar evolution models. To resolve this issue, the number of this type of object has been rapidly increased through the development of worldwide surveys. Taking advantage of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope survey, 44 new Li-rich giants are reported, which are confirmed with high-resolution observations. Based on the high-resolution and high signal-to-noise spectra, we derived the atmospheric parameters and elemental abundances with the spectral synthesis method. We performed a detailed analysis of their evolutionary stages, infrared excess, projected rotational velocity (vsini), and stellar population. We find that (1) the Li-rich giants concentrate at the evolutionary status of the red giant branch bump, red clump, and asymptotic giant branch; (2) three of them are fast rotators and none exhibit infrared excess. Our results imply that the origins of Li enrichment are most likely to be associated with the extra mixing in the stellar interior, and the external sources might only make a minor contribution. Moreover, various Li-rich episodes take place at different evolutionary stages.
103. Homogeneous study of Herbig Ae/Be stars
ID:
ivo://CDS.VizieR/J/A+A/650/A182
Title:
Homogeneous study of Herbig Ae/Be stars
Short Name:
J/A+A/650/A182
Date:
22 Feb 2022
Publisher:
CDS
Description:
Herbig Ae/Be stars (HAeBes) have so far been studied based on relatively small samples that are scattered throughout the sky. Their fundamental stellar and circumstellar parameters and statistical properties were derived with heterogeneous approaches before Gaia. Our main goal is to contribute to the study of HAeBes from the largest sample of such sources to date, for which stellar and circumstellar properties have been determined homogeneously from the analysis of the spectral energy distributions (SEDs) and Gaia EDR3 parallaxes and photometry. Multiwavelength photometry was compiled for 209 bona fide HAeBes for which Gaia EDR3 distances were estimated. Using the Virtual Observatory SED Analyser (VOSA), photospheric models were fit to the optical SEDs to derive stellar parameters, and the excesses at infrared (IR) and longer wavelengths were characterized to derive several circumstellar properties. A statistical analysis was carried out to show the potential use of such a large dataset. The stellar temperature, luminosity, radius, mass, and age were derived for each star based on optical photometry. In addition, their IR SEDs were classified according to two different schemes, and their mass accretion rates, disk masses, and the sizes of the inner dust holes were also estimated uniformly. The initial mass function fits the stellar mass distribution of the sample within 2<M_star_/M_{sun}_<12. In this aspect, the sample is therefore representative of the HAeBe regime and can be used for statistical purposes when it is taken into account that the boundaries are not well probed. Our statistical study does not reveal any connection between the SED shape from the Meeus et al., 2001A&A...365..476M classification and the presence of transitional disks, which are identified here based on the SEDs that show an IR excess starting at the K band or longer wavelengths. In contrast, only ~28% of the HAeBes have transitional disks, and the related dust disk holes are more frequent in HBes than in HAes (~34% vs 15%). The relatively small inner disk holes and old stellar ages estimated for most transitional HAes indicate that photoevaporation cannot be the main mechanism driving disk dissipation in these sources. In contrast, the inner disk holes and ages of most transitional HBes are consistent with the photoevaporation scenario, although these results alone do not unambiguously discard other disk dissipation mechanisms. The complete dataset is available online through a Virtual Observatory- compliant archive, representing the most recent reference for statistical studies on the HAeBe regime. VOSA is a complementary tool for the future characterization of newly identified HAeBes.
104. HST far-UV survey of H2 emission of T Tau stars
ID:
ivo://CDS.VizieR/J/ApJ/756/171
Title:
HST far-UV survey of H2 emission of T Tau stars
Short Name:
J/ApJ/756/171
Date:
21 Oct 2021
Publisher:
CDS
Description:
The formation timescale and final architecture of exoplanetary systems are closely related to the properties of the molecular disks from which they form. Observations of the spatial distribution and lifetime of the molecular gas at planet-forming radii (a<10AU) are important for understanding the formation and evolution of exoplanetary systems. Toward this end, we present the largest spectrally resolved survey of H_2_ emission around low-mass pre-main-sequence stars compiled to date. We use a combination of new and archival far-ultraviolet spectra from the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph instruments on the Hubble Space Telescope to sample 34 T Tauri stars (27 actively accreting Classical T Tauri Stars and 7 non-accreting Weak-lined T Tauri Stars) with ages ranging from ~1 to 10Myr. We observe fluorescent H_2_emission, excited by Ly{alpha} photons, in 100% of the accreting sources, including all of the transitional disks in our sample (CS Cha, DM Tau, GM Aur, UX Tau A, LkCa 15, HD 135344B, and TW Hya). The spatial distribution of the emitting gas is inferred from spectrally resolved H_2_ line profiles. Some of the emitting gas is produced in outflowing material, but the majority of H_2_ emission appears to originate in a rotating disk. For the disk-dominated targets, the H_2_ emission originates predominately at a<~3AU. The emission line widths and inner molecular radii are found to be roughly consistent with those measured from mid-IR CO spectra.
105. HST observations of nearby core-collapse SNe
ID:
ivo://CDS.VizieR/J/ApJ/860/39
Title:
HST observations of nearby core-collapse SNe
Short Name:
J/ApJ/860/39
Date:
21 Oct 2021
Publisher:
CDS
Description:
We age-date the stellar populations associated with 12 historic nearby core-collapse supernovae (CCSNe) and two supernova impostors; from these ages, we infer their initial masses and associated uncertainties. To do this, we have obtained new Hubble Space Telescope imaging covering these CCSNe. Using these images, we measure resolved stellar photometry for the stars surrounding the locations of the SNe. We then fit the color-magnitude distributions of this photometry with stellar evolution models to determine the ages of any young existing populations present. From these age distributions, we infer the most likely progenitor masses for all of the SNe in our sample. We find ages between 4 and 50Myr, corresponding to masses from 7.5 to 59M_{sun}_. There were no SNe that lacked a local young population. Our sample contains four SNe Ib/c; their masses have a wide range of values, suggesting that the progenitors of stripped-envelope SNe are binary systems. Both impostors have masses constrained to be <~7.5M_{sun}_. In cases with precursor imaging measurements, we find that age-dating and precursor imaging give consistent progenitor masses. This consistency implies that, although the uncertainties for each technique are significantly different, the results of both are reliable to the measured uncertainties. We combine these new measurements with those from our previous work and find that the distribution of 25 core-collapse SNe progenitor masses is consistent with a standard Salpeter power-law mass function, no upper mass cutoff, and an assumed minimum mass for core-collapse of 7.5M_{sun}_. The distribution is consistent with a minimum mass <9.5M_{sun}_.
106. IC1805 YSOs
ID:
ivo://CDS.VizieR/J/MNRAS/468/2684
Title:
IC1805 YSOs
Short Name:
J/MNRAS/468/2684
Date:
21 Oct 2021
Publisher:
CDS
Description:
W4 is a giant HII region ionized by the OB stars of the cluster IC 1805. The HII region/cluster complex has been a subject of numerous investigations as it is an excellent laboratory for studying the feedback effect of massive stars on the surrounding region. However, the low-mass stellar content of the cluster IC 1805 remains poorly studied till now. With the aim to unravel the low-mass stellar population of the cluster, we present the results of a multiwavelength study based on deep optical data obtained with the Canada-France-Hawaii Telescope, infrared data from Two Micron All Sky Survey and SpitzerSpace Telescope and X-ray data from ChandraSpace Telescope. The present optical data set is complete enough to detect stars down to 0.2M_{sun}_, which is the deepest optical observation so far for the cluster. We identified 384 candidate young stellar objects (YSOs; 101 Class I/II and 283 Class III) within the cluster using various colour-colour and colour-magnitude diagrams. We inferred the mean age of the identified YSOs to be ~2.5Myr and mass in the range 0.3-2.5M_{sun}_. The mass function of our YSO sample has a power-law index of -1.23+/-0.23, close to the Salpeter value (-1.35), and consistent with those of other star-forming complexes. We explored the disc evolution of the cluster members and found that the disc-less sources are relatively older compared to the disc bearing YSO candidates. We examined the effect of high-mass stars on the circumstellar discs and within uncertainties, the influence of massive stars on the disc fraction seems to be insignificant. We also studied the spatial correlation of the YSOs with the distribution of gas and dust of the complex to conclude that IC 1805 would have formed in a large filamentary cloud.
107. Imaging survey of Spitzer-detected debris disks
ID:
ivo://CDS.VizieR/J/AJ/154/245
Title:
Imaging survey of Spitzer-detected debris disks
Short Name:
J/AJ/154/245
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe a joint high-contrast imaging survey for planets at the Keck and Very Large Telescope of the last large sample of debris disks identified by the Spitzer Space Telescope. No new substellar companions were discovered in our survey of 30 Spitzer-selected targets. We combine our observations with data from four published surveys to place constraints on the frequency of planets around 130 debris disk single stars, the largest sample to date. For a control sample, we assembled contrast curves from several published surveys targeting 277 stars that do not show infrared excesses. We assumed a double power-law distribution in mass and semimajor axis (SMA) of the form f(m,a)=Cm^{alpha}^{alpha}^{beta}^, where we adopted power-law values and logarithmically flat values for the mass and SMA of planets. We find that the frequency of giant planets with masses 5-20 M_Jup_ and separations 10-1000 au around stars with debris disks is 6.27% (68% confidence interval 3.68%-9.76%), compared to 0.73% (68% confidence interval 0.20%-1.80%) for the control sample of stars without disks. These distributions differ at the 88% confidence level, tentatively suggesting distinctness of these samples.
108. International Deep Planet Survey results
ID:
ivo://CDS.VizieR/J/A+A/594/A63
Title:
International Deep Planet Survey results
Short Name:
J/A+A/594/A63
Date:
21 Oct 2021
Publisher:
CDS
Description:
Radial velocity and transit methods are effective for the study of short orbital period exoplanets but they hardly probe objects at large separations for which direct imaging can be used. We carried out the international deep planet survey of 292 young nearby stars to search for giant exoplanets and determine their frequency. We developed a pipeline for a uniform processing of all the data that we have recorded with NIRC2/KeckII, NIRI/Gemini North, NICI/Gemini South, NACO/VLT for 14 years. The pipeline first applies cosmetic corrections and then reduces the speckle intensity to enhance the contrast in the images. The main result of the international deep planet survey is the discovery of the HR 8799 exoplanets. We also detected 59 visual multiple systems including 16 new binary stars and 2 new triple stellar systems, as well as 2279 point-like sources. We used Monte-Carlo simulations and the Bayesian' theorem to determine that 1.05% (+2.80% and -0.70%) of stars harbor at least one giant planet between 0.5 and 14M_{Jup}_, and between 20 and 300AU. This result is obtained assuming uniform distributions of planet masses and semi-major axes. If we consider power law distributions as measured for close-in planets instead, the derived frequency is 2.30% (+5.95% and -1.55%), reminding the strong impact of assumptions on Monte-Carlo output distributions. We also find no evidence that the derived frequency depends on the mass of the hosting star whereas it does for close-in planets. The international deep planet survey provides a database of confirmed background sources that may be useful for other exoplanet direct imaging surveys. It also puts new constraints on the number of stars with at least one giant planet reducing by a factor of two the frequencies derived by almost all previous works.
109. Keck HIRES obs. of 245 subgiants (retired A stars)
ID:
ivo://CDS.VizieR/J/ApJ/860/109
Title:
Keck HIRES obs. of 245 subgiants (retired A stars)
Short Name:
J/ApJ/860/109
Date:
21 Oct 2021
Publisher:
CDS
Description:
Exoplanet surveys of evolved stars have provided increasing evidence that the formation of giant planets depends not only on stellar metallicity ([Fe/H]) but also on the mass (M*). However, measuring accurate masses for subgiants and giants is far more challenging than it is for their main-sequence counterparts, which has led to recent concerns regarding the veracity of the correlation between stellar mass and planet occurrence. In order to address these concerns, we use HIRES spectra to perform a spectroscopic analysis on a sample of 245 subgiants and derive new atmospheric and physical parameters. We also calculate the space velocities of this sample in a homogeneous manner for the first time. When reddening corrections are considered in the calculations of stellar masses and a -0.12M_{sun}_ offset is applied to the results, the masses of the subgiants are consistent with their space velocity distributions, contrary to claims in the literature. Similarly, our measurements of their rotational velocities provide additional confirmation that the masses of subgiants with M*>=1.6M_{sun}_ (the "retired A stars") have not been overestimated in previous analyses. Using these new results for our sample of evolved stars, together with an updated sample of FGKM dwarfs, we confirm that giant planet occurrence increases with both stellar mass and metallicity up to 2.0M_{sun}_. We show that the probability of formation of a giant planet is approximately a one-to-one function of the total amount of metals in the protoplanetary disk M* 10^[Fe/H]. This correlation provides additional support for the core accretion mechanism of planet formation.
110. Kepler asteroseismic LEGACY sample. II.
ID:
ivo://CDS.VizieR/J/ApJ/835/173
Title:
Kepler asteroseismic LEGACY sample. II.
Short Name:
J/ApJ/835/173
Date:
21 Oct 2021
Publisher:
CDS
Description:
We use asteroseismic data from the Kepler satellite to determine fundamental stellar properties of the 66 main-sequence targets observed for at least one full year by the mission. We distributed tens of individual oscillation frequencies extracted from the time series of each star among seven modeling teams who applied different methods to determine radii, masses, and ages for all stars in the sample. Comparisons among the different results reveal a good level of agreement in all stellar properties, which is remarkable considering the variety of codes, input physics, and analysis methods employed by the different teams. Average uncertainties are of the order of ~2% in radius, ~4% in mass, and ~10% in age, making this the best-characterized sample of main-sequence stars available to date. Our predicted initial abundances and mixing-length parameters are checked against inferences from chemical enrichment laws {Delta}Y/{Delta}Z and predictions from 3D atmospheric simulations. We test the accuracy of the determined stellar properties by comparing them to the Sun, angular diameter measurements, Gaia parallaxes, and binary evolution, finding excellent agreement in all cases and further confirming the robustness of asteroseismically determined physical parameters of stars when individual frequencies of oscillation are available. Baptised as the Kepler dwarfs LEGACY sample, these stars are the solar-like oscillators with the best asteroseismic properties available for at least another decade. All data used in this analysis and the resulting stellar parameters are made publicly available for the community.

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