- ID:
- ivo://CDS.VizieR/J/ApJ/886/100
- Title:
- High-mass white dwarfs in Gaia DR2
- Short Name:
- J/ApJ/886/100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Revealed by Gaia DR2, the Q branch is a narrow and prominent branch of white dwarf overdensity on the H-R diagram. We find that there are significantly more fast-moving white dwarfs on the Q branch, which have very old true ages but young photometric ages. This age discrepancy suggests a cooling anomaly in some white dwarfs on the Q branch, posing a challenge to current white dwarf cooling models. We tabulate the information of nearby high-mass white dwarfs (d<250, 1.08<m_WD<1.23), which is used to investigate the Q branch and its physical origin in Cheng et al. (2019). This table contains the WD name, photometry and astrometry from Gaia DR2, H-R diagram coordinates and transverse velocity that we derive, and spectral information from Montreal White Dwarf Database (MWDD).
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- ID:
- ivo://CDS.VizieR/J/A+A/561/A7
- Title:
- High-precision abundances for stars with planets
- Short Name:
- J/A+A/561/A7
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Elemental abundance studies of solar twin stars suggest that the solar chemical composition contains signatures of the formation of terrestrial planets in the solar system, namely small but significant depletions of the refractory elements. To test this hypothesis, we study stars which, compared to solar twins, have less massive convective envelopes (therefore increasing the amplitude of the predicted effect) or are, arguably, more likely to host planets (thus increasing the frequency of signature detections). We measure relative atmospheric parameters and elemental abundances of a late-F type dwarf sample (52 stars) and a sample of metal-rich solar analogs (59 stars). We detect refractory-element depletions with amplitudes up to about 0.15dex. The distribution of depletion amplitudes for stars known to host gas giant planets is not different from that of the rest of stars. The maximum amplitude of depletion increases with effective temperature from 5650K to 5950K, while it appears to be constant for warmer stars (up to 6300K). The depletions observed in solar twin stars have a maximum amplitude that is very similar to that seen here for both of our samples. Gas giant planet formation alone cannot explain the observed distributions of refractory-element depletions, leaving the formation of rocky material as a more likely explanation of our observations. More rocky material is necessary to explain the data of solar twins than metal-rich stars, and less for warm stars. However, the sizes of the stars' convective envelopes at the time of planet formation could be regulating these amplitudes. Our results could be explained if disk lifetimes were shorter in more massive stars, as independent observations indeed seem to suggest.
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/159/197
- Title:
- HIRES radial velocities of HD9446, HD43691 & HD179079
- Short Name:
- J/AJ/159/197
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Transit Ephemeris Refinement and Monitoring Survey is a project that aims to detect transits of intermediate-long period planets by refining orbital parameters of the known radial velocity planets using additional data from ground-based telescopes, calculating a revised transit ephemeris for the planet, then monitoring the planet host star during the predicted transit window. Here we present the results from three systems that had high probabilities of transiting planets: HD9446b and c, HD43691b, and HD179079b. We provide new radial velocity (RV) measurements that are then used to improve the orbital solution for the known planets. We search the RV data for indications of additional planets in orbit and find that HD9446 shows a strong linear trend of 4.8{sigma}. Using the newly refined planet orbital solutions, which include a new best-fit solution for the orbital period of HD9446c, and an improved transit ephemerides, we found no evidence of transiting planets in the photometry for each system. Transits of HD9446b can be ruled out completely and transits HD9446c and HD43691b can be ruled out for impact parameters up to b=0.5778 and b=0.898, respectively, due to gaps in the photometry. A transit of HD179079b cannot be ruled out, however, due to the relatively small size of this planet compared to the large star and thus low signal to noise. We determine properties of the three host stars through spectroscopic analysis and find through photometric analysis that HD9446 exhibits periodic variability.
- ID:
- ivo://CDS.VizieR/J/ApJ/785/126
- Title:
- HIRES radial velocity measurements
- Short Name:
- J/ApJ/785/126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we search for distant massive companions to known transiting gas giant planets that may have influenced the dynamical evolution of these systems. We present new radial velocity observations for a sample of 51 planets obtained using the Keck HIRES instrument, and find statistically significant accelerations in fifteen systems. Six of these systems have no previously reported accelerations in the published literature: HAT-P-10, HAT-P-22, HAT-P-29, HAT-P-32, WASP-10, and XO-2. We combine our radial velocity fits with Keck NIRC2 adaptive optics (AO) imaging data to place constraints on the allowed masses and orbital periods of the companions responsible for the detected accelerations. The estimated masses of the companions range between 1-500 M_Jup_, with orbital semi-major axes typically between 1-75 AU. A significant majority of the companions detected by our survey are constrained to have minimum masses comparable to or larger than those of the transiting planets in these systems, making them candidates for influencing the orbital evolution of the inner gas giant. We estimate a total occurrence rate of 51%+/-10% for companions with masses between 1-13 M_Jup_ and orbital semi-major axes between 1-20 AU in our sample. We find no statistically significant difference between the frequency of companions to transiting planets with misaligned or eccentric orbits and those with well-aligned, circular orbits. We combine our expanded sample of radial velocity measurements with constraints from transit and secondary eclipse observations to provide improved measurements of the physical and orbital characteristics of all of the planets included in our survey.
- ID:
- ivo://CDS.VizieR/J/A+A/501/563
- Title:
- HKs photometry in the Arches cluster
- Short Name:
- J/A+A/501/563
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The massive Arches cluster near the Galactic center should be an ideal laboratory for investigating massive star formation under extreme conditions. But it comes at a high price: the cluster is hidden behind several tens of magnitudes of visual extinction. Severe crowding requires space or AO-assisted instruments to resolve the stellar populations, and even with the best instruments interpreting the data is far from direct. Several investigations using NICMOS and the most advanced AO imagers on the ground revealed an overall top-heavy IMF for the cluster, with a very flat IMF near the center. There are several effects, however, that could potentially bias these results, in particular the strong differential extinction and the problem of transforming the observations into a standard photometric system in the presence of strong reddening. We present new observations obtained with the NAOS-Conica (NACO) AO-imager on the VLT. The problem of photometric transformation is avoided by working in the natural photometric system of NACO, and we use a Bayesian approach to determine masses and reddenings from the broad-band IR colors. A global value of Gamma=-1.1+/-0.2 for the high-mass end (M>10M_{sun}_) of the IMF is obtained, and we conclude that a power law of Salpeter slope cannot be discarded for the Arches cluster. The flattening of the IMF towards the center is confirmed, but is less severe than previously thought. We find Gamma=-0.88+/-0.20, which is incompatible with previous determinations. Within 0.4pc we derive a total mass of ~2.0(+/-0.6)x10^4^M_{sun}_ for the cluster and a central mass density rho=2(+/-0.4)x10^5^M_{sun}_/pc^3^ that confirms Arches as the densest known young massive cluster in the Milky Way.
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/162/188
- Title:
- Hot degenerates in the MCT survey. III.
- Short Name:
- J/AJ/162/188
- Date:
- 21 Mar 2022 00:13:43
- Publisher:
- CDS
- Description:
- We present optical spectra of 144 white dwarfs detected in the Montreal-Cambridge-Tololo colorimetric survey, including 120 DA, 12 DB, 4 DO, 1 DQ, and 7 DC stars. We also perform a model atmosphere analysis of all objects in our sample using the so-called spectroscopic technique, or the photometric technique in the case of DC white dwarfs. The main objective of this paper is to contribute to the ongoing effort of confirming spectroscopically all white dwarf candidates in the Gaia survey, in particular in the southern hemisphere. All our spectra are made available in the Montreal White Dwarf Database.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/63
- Title:
- How to constrain your M dwarf. II. Nearby binaries
- Short Name:
- J/ApJ/871/63
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mass-luminosity relation for late-type stars has long been a critical tool for estimating stellar masses. However, there is growing need for both a higher-precision relation and a better understanding of systematic effects (e.g., metallicity). Here we present an empirical relationship between M_Ks_ and M_*_ spanning 0.075M_{sun}_<M_*_<0.70M_{sun}_. The relation is derived from 62 nearby binaries, whose orbits we determine using a combination of near infra-red (Keck/NIRC2) imaging, archival adaptive optics data, and literature astrometry. From their orbital parameters, we determine the total mass of each system, with a precision better than 1% in the best cases. We use these total masses, in combination with resolved Ks magnitudes and system parallaxes, to calibrate the M_Ks_-M_*_ relation. The resulting posteriors can be used to determine masses of single stars with a precision of 2%-3%, which we confirm by testing the relation on stars with individual dynamical masses from the literature. The precision is limited by scatter around the best-fit relation beyond measured M_*_ uncertainties, perhaps driven by intrinsic variation in the M_Ks_-M_*_ relation or underestimated uncertainties in the input parallaxes. We find that the effect of [Fe/H] on the M_Ks_-M_*_ relation is likely negligible for metallicities in the solar neighborhood (0.0%{+/-}2.2% change in mass per dex change in [Fe/H]). This weak effect is consistent with predictions from the Dartmouth Stellar Evolution Database, but inconsistent with those from modules for experiments in stellar astrophysics (MESA) Isochrones and Stellar Tracks (MIST) (at 5{sigma}). A sample of binaries with a wider range of abundances will be required to discern the importance of metallicity in extreme populations (e.g., in the Galactic halo or thick disk).
- ID:
- ivo://CDS.VizieR/J/ApJ/823/49
- Title:
- HST/COS observations of 7 white dwarfs
- Short Name:
- J/ApJ/823/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The search for transiting habitable exoplanets has broadened to include several types of stars that are smaller than the Sun in an attempt to increase the observed transit depth and hence the atmospheric signal of the planet. Of all spectral types, white dwarfs (WDs) are the most favorable for this type of investigation. The fraction of WDs that possess close-in rocky planets is unknown, but several large angle stellar surveys have the photometric precision and cadence to discover at least one if they are common. Ultraviolet observations of WDs may allow for detection of molecular oxygen or ozone in the atmosphere of a terrestrial planet. We use archival Hubble Space Telescope data from the Cosmic Origins Spectrograph to search for transiting rocky planets around UV-bright WDs. In the process, we discovered unusual variability in the pulsating WD GD 133, which shows slow sinusoidal variations in the UV. While we detect no planets around our small sample of targets, we do place stringent limits on the possibility of transiting planets, down to sub-lunar radii. We also point out that non-transiting small planets in thermal equilibrium are detectable around hotter WDs through infrared excesses, and identify two candidates.
