- ID:
- ivo://CDS.VizieR/J/ApJ/878/21
- Title:
- Vertical motions of APOGEE & Gaia red clump stars
- Short Name:
- J/ApJ/878/21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It has long been known that the vertical motions of Galactic disk stars increase with stellar age, commonly interpreted as vertical heating through orbit scattering. Here we map the vertical actions of disk stars as a function of age ({tau}<=8Gyr) and across a large range of Galactocentric radii, R_GC_, drawing on APOGEE and Gaia data. We fit J_z_(R_GC,{tau}_) as a combination of the vertical action at birth, J_z,0_, and the subsequent heating {Delta}J_z,1Gyr_(R_GC_), which scales as {tau}^{gamma}(R_GC_)^. The inferred birth temperature, J_z,0_(R_GC_) is 1kpc.km/s for 3kpc<R_GC_<10kpc, consistent with the ISM velocity dispersion, but it rapidly rises outward, to 8kpc.km/s for R_GC_=14kpc, likely reflecting the stars' birth in a warped or flared gas disk. We find the heating rate {Delta}J_z,1Gyr_ to be modest and nearly constant across all radii, 1.6kpc.km/s/Gyr. The stellar age dependence {gamma} gently grows with Galactocentric radius, from {gamma}~1 for R_GC_<~R_{sun}_ to {gamma}~1.3 at R_GC_=14kpc. The observed J_z_-{tau} relation at all radii is considerably steeper ({gamma}>~1) than the time dependence theoretically expected from orbit scattering, J_z_{propto}t^0.5^. We illustrate how this conundrum can be resolved if we also account for the fact that at earlier epochs, the scatterers were more common, and the restoring force from the stellar disk surface mass density was low. Our analysis may reinstate gradual orbital scattering as a plausible and viable mechanism to explain the age-dependent vertical motions of disk stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/573/A126
- Title:
- VLT/NaCo Large program I. Sample
- Short Name:
- J/A+A/573/A126
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young, close stars are ideal targets for searching planets using the direct imaging technique. The determination of stellar parameters is crucial for the interpretation of imaging survey results, particularly since the luminosity of substellar objects has a strong dependence on system age. We have conducted a large program with NaCo at the VLT to search for planets and brown dwarfs in wide orbits around 86 stars. A large fraction of the targets observed with NaCo were poorly investigated in the literature. We performed a study to characterize the fundamental properties (age, distance, and mass) of the stars in our sample. To improve target age determinations, we compiled and analyzed a complete set of age diagnostics. We measured spectroscopic parameters and age diagnostics using dedicated observations acquired with FEROS and CORALIE spectrographs at La Silla Observatory. We also made extensive use of archival spectroscopic data and the results that are available in the literature. Additionally, we exploited photometric time-series, which are available in ASAS and Super-WASP archives, to derive a rotational period for a large fraction of our program stars. We provided updated characterization of all the targets observed in the VLT NaCo Large program, a survey designed to probe the occurrence of exoplanets and brown dwarfs in wide orbits. The median distance and age of our program stars are 64pc and 100Myr, respectively. Nearly all the stars have masses between 0.70 and 1.50M_{sun}_, with a median value of 1.01M_{sun}_. The typical metallicity is close to solar with a dispersion that is smaller than that of samples usually observed in radial velocity surveys. Several stars are confirmed or proposed here to be members of close young moving groups. Eight spectroscopic binaries are identified.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A3
- Title:
- VLT/NaCo Large program. IV. Statistical analysis
- Short Name:
- J/A+A/603/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Understanding the formation and evolution of giant planets (>1M_Jup_) at wide orbital separation (>5AU) is one of the goals of direct imaging. Over the past 15 years, many surveys have placed strong constraints on the occurrence rate of wide-orbit giants, mostly based on non-detections, but very few have tried to make a direct link with planet formation theories. In the present work, we combine the results of our previously published VLT/NaCo large program with the results of 12 past imaging surveys to constitute a statistical sample of 199 FGK stars within 100 pc, including three stars with sub-stellar companions. Using Monte Carlo simulations and assuming linear flat distributions for the mass and semi-major axis of planets, we estimate the sub-stellar companion frequency to be within 0.75-5.70% at the 68% confidence level (CL) within 20-300AU and 0.5-75M_Jup_, which is compatible with previously published results. We also compare our results with the predictions of state-of-the-art population synthesis models based on the gravitational instability (GI) formation scenario with and without scattering. We estimate that in both the scattered and non-scattered populations, we would be able to detect more than 30% of companions in the 1-75M_Jup_ range (95% CL). With the three sub-stellar detections in our sample, we estimate the fraction of stars that host a planetary system formed by GI to be within 1.0-8.6% (95% CL). We also conclude that even though GI is not common, it predicts a mass distribution of wide-orbit massive companions that is much closer to what is observed than what the core accretion scenario predicts. Finally, we associate the present paper with the release of the Direct Imaging Virtual Archive (DIVA), a public database that aims at gathering the results of past, present, and future direct imaging surveys.
- ID:
- ivo://CDS.VizieR/J/AJ/138/1681
- Title:
- WD within 20pc of the Sun
- Short Name:
- J/AJ/138/1681
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the kinematical properties, distribution of spectroscopic subtypes, and stellar population subcomponents of the white dwarfs within 20pc of the Sun. We find no convincing evidence of halo white dwarfs in the total 20pc sample of 129 white dwarfs nor is there convincing evidence of genuine thick disk subcomponent members within 20 parsecs. Virtually, the entire 20pc sample likely belongs to the thin disk. The total DA to non-DA ratio of the 20pc sample is 1.6, a manifestation of deepening envelope convection which transforms DA stars with sufficiently thin H surface layers into non-DAs. The addition of five new stars to the 20pc sample yields a revised local space density of white dwarfs of (4.9+/-0.5)x10^-3^pc^-3^ and a corresponding mass density of (3.3+/-0.3)x10^-3^M_{sun}_pc^-3^. We find that at least 15% of the white dwarfs within 20 parsecs of the Sun (the DAZ and DZ stars) have photospheric metals that possibly originate from accretion of circumstellar material (debris disks) around them. If this interpretation is correct, this suggests the possibility that the same percentage have planets or asteroid-like bodies orbiting them.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/2506
- Title:
- White dwarf candidates in DECam first field
- Short Name:
- J/MNRAS/462/2506
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from a minute cadence survey of a 3deg^2^ field obtained with the Dark Energy Camera. We imaged part of the Canada-France-Hawaii Telescope Legacy Survey area over eight half-nights. We use the stacked images to identify 111 high proper motion white dwarf candidates with g<=24.5mag and search for eclipse-like events and other sources of variability. We find a new g=20.64mag pulsating ZZ Ceti star with pulsation periods of 11-13min. However, we do not find any transiting planetary companions in the habitable zone of our target white dwarfs. Given the probability of eclipses of 1 per cent and our observing window from the ground, the non-detection of such companions in this first field is not surprising. Minute cadence DECam observations of additional fields will provide stringent constraints on the frequency of planets in the white dwarf habitable zone.
- ID:
- ivo://CDS.VizieR/J/MNRAS/469/2102
- Title:
- White dwarf population from the SDSS DR12
- Short Name:
- J/MNRAS/469/2102
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use the Sloan Digital Sky Survey Data Release 12, which is the largest available white dwarf catalogue to date, to study the evolution of the kinematical properties of the population of white dwarfs in the Galactic disc. We derive masses, ages, photometric distances and radial velocities for all white dwarfs with hydrogen-rich atmospheres. For those stars for which proper motions from the USNO-B1 catalogue are available, the true three-dimensional components of the stellar space velocity are obtained. This subset of the original sample comprises 20 247 objects, making it the largest sample of white dwarfs with measured three-dimensional velocities. Furthermore, the volume probed by our sample is large, allowing us to obtain relevant kinematical information. In particular, our sample extends from a Galactocentric radial distance R_G_=7.8 to 9.3kpc, and vertical distances from the Galactic plane ranging from Z=-0.5 to 0.5kpc. We examine the mean components of the stellar three-dimensional velocities, as well as their dispersions with respect to the Galactocentric and vertical distances. We confirm the existence of a mean Galactocentric radial velocity gradient, {partial}<V_R_>/{partial}R_G_=-3+/-5km/s/. We also confirm north-south differences in <V_z_> . Specifically, we find that white dwarfs with Z>0 (in the North Galactic hemisphere) have <V_z_><0, while the reverse is true for white dwarfs with Z<0. The age-velocity dispersion relation derived from the present sample indicates that the Galactic population of white dwarfs may have experienced an additional source of heating, which adds to the secular evolution of the Galactic disc.
- ID:
- ivo://CDS.VizieR/J/MNRAS/457/1988
- Title:
- White dwarfs in Galactic plane
- Short Name:
- J/MNRAS/457/1988
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigated the prospects for systematic searches of white dwarfs at low Galactic latitudes, using the VLT Survey Telescope H{alpha} Photometric Survey of the Galactic plane and Bulge (VPHAS+). We targeted 17 white dwarf candidates along sightlines of known open clusters, aiming to identify potential cluster members. We confirmed all the 17 white dwarf candidates from blue/optical spectroscopy, and we suggest five of them to be likely cluster members. We estimated progenitor ages and masses for the candidate cluster members, and compare our findings to those for other cluster white dwarfs. A white dwarf in NGC 3532 is the most massive known cluster member (1.13M_{sun}_), likely with an oxygen-neon core, for which we estimate an M_{sun}_ progenitor, close to the mass-divide between white dwarf and neutron star progenitors. A cluster member in Ruprecht 131 is a magnetic white dwarf, whose progenitor mass exceeded 2-3M_{sun}_. We stress that wider searches, and improved cluster distances and ages derived from data of the ESA Gaia mission, will advance the understanding of the mass-loss processes for low- to intermediate-mass stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/437/185
- Title:
- W UMa-type contact binaries ages and masses
- Short Name:
- J/MNRAS/437/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recently, our understanding of the origin of W UMa-type contact binaries has become clearer. Initial masses of their components were successfully estimated by Yildiz and Dogan using a new method mainly based on observational properties of overluminous secondary components. In this paper, we continue to discuss the results and make computations for age and orbital evolution of these binaries. It is shown that the secondary mass, according to its luminosity, also successfully predicts the observed radius. While the current mass of the primary component is determined by initial masses, the current secondary mass is also a function of initial angular momentum. We develop methods to compute the age of A- and W-subtype W UMa-type contact binaries in terms of initial masses and mass according to the luminosity of the secondaries. Comparisons of our results with the mean ages from kinematic properties of these binaries and data pertaining to contact binaries in open and globular clusters have increased our confidence on this method. The mean ages of both A- and W-subtype contact binaries are found as 4.4 and 4.6Gyr, respectively. From kinematic studies, these ages are given as 4.5 and 4.4Gyr, respectively. We also compute orbital properties of A-subtype contact binaries at the time of the first overflow. Initial angular momentum of these binaries is computed by comparing them with the well-known detached binaries. The angular momentum loss rate derived in the present study for the detached phase is in very good agreement with the semi-empirical rates available in the literature. In addition to the limitations on the initial masses of W UMa-type contact binaries, it is shown that the initial period of these binaries is less than about 4.45d.
- ID:
- ivo://CDS.VizieR/J/A+A/609/A127
- Title:
- X-ray sources in CMa OB1
- Short Name:
- J/A+A/609/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Canis Major OB1 association has an intriguing scenario of star formation, especially in the region called Canis Major R1 (CMa R1) traditionally assigned to a reflection nebula, but in reality an ionized region. This work is focussed on the young stellar population associated with CMa R1, for which our previous results from ROSAT, optical, and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star formation episodes. The X-ray data allow the detected sources to be characterized according to hardness ratios, light curves, and spectra. Estimates of mass and age were obtained from the 2MASS catalogue and used to define a complete subsample of stellar counterparts for statistical purposes. A catalogue of 387 XMM-Newton sources is provided, of which 78% are confirmed as members or probable members of the CMa R1 association. Flares (or similar events) were observed for 13 sources and the spectra of 21 bright sources could be fitted by a thermal plasma model. Mean values of fits parameters were used to estimate X-ray luminosities. We found a minimum value of log(L_X_[erg/s])=29.43, indicating that our sample of low-mass stars (M*<=0.5 M_{sun}_), which are faint X-ray emitters, is incomplete. Among the 250 objects selected as our complete subsample (defining our "best sample"), 171 are found to the east of the cloud, near Z CMa and dense molecular gas, of which 50% of them are young (<5Myr) and 30% are older (>10Myr). The opposite happens to the west, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% are young and 50% are older. These findings confirm that a first episode of distributed star formation occurred in the whole studied region ~10Myr ago and dispersed the molecular gas, while a second, localized episode (<5Myr) took place in the regions where molecular gas is still present.
- ID:
- ivo://CDS.VizieR/J/ApJ/841/92
- Title:
- Young massive star clusters in 2 LEGUS galaxies
- Short Name:
- J/ApJ/841/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of the effective (half-light) radii and other structural properties of a systematically selected sample of young, massive star clusters (>=5x10^3^M_{sun}_ and <=200Myr) in two nearby spiral galaxies, NGC 628 and NGC 1313. We use Hubble Space Telescope (HST) WFC3/UVIS and archival ACS/WFC data obtained by the Legacy Extragalactic UV Survey (LEGUS), an HST Treasury Program. We measure effective radii with GALFIT, a two- dimensional image-fitting package, and with a new technique to estimate effective radii from the concentration index of observed clusters. The distribution of effective radii from both techniques spans ~0.5-10pc and peaks at 2-3pc for both galaxies. We find slight positive correlations between effective radius and cluster age in both galaxies, but no significant relationship between effective radius and galactocentric distance. Clusters in NGC 1313 display a mild increase in effective radius with cluster mass, but the trend disappears when the sample is divided into age bins. We show that the vast majority of the clusters in both galaxies are much older than their dynamical times, suggesting they are gravitationally bound objects. We find that about half of the clusters in NGC 628 are underfilling their Roche lobes, based on their Jacobi radii. Our results suggest that the young, massive clusters in NGC 628 and NGC 1313 are expanding, due to stellar mass loss or two-body relaxation, and are not significantly influenced by the tidal fields of their host galaxies.
