- ID:
- ivo://CDS.VizieR/J/PAZh/38/776
- Title:
- Complete sample of OB stars within 350pc
- Short Name:
- J/PAZh/38/776
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The sample of 37485 suspected OB stars selected by Gontcharov (2008AstL...34....7G) from the Tycho-2 catalogue has been cleaned of the stars that are not of spectral types OV-A0V. For this purpose, the apparent magnitude VT from Tycho-2, the absolute magnitude MVT calibrated as a function of the dereddened color index (BT-VT)0, the interstellar extinction AVT calculated from the 3D analytical model by Gontcharov (2009AstL...35..780G) as a function of the Galactic coordinates, and the photometric distance Rph calculated as a function of VT, M_VT_, and A_VT_ have been reconciled in an iterative process. The 20514 stars that passed the iterations have (BT-VT)_0_<0 and M_VT_>-5 and are considered as a sample of OV-A0V stars complete within 350 pc of the Sun. Based on the theoretical relation between the dereddened color and age of the stars, the derived sample has been divided into three subsamples: (BT-VT)_0_< -0.2, -0.2<(BT-VT)_0_< -0.1, and -0.1<(BT-VT)_0_<0, younger than 100, 100-200, and 200-400 Myr, respectively. The spatial distribution of all 20514 stars and the kinematics analyzed for more than 1500 stars with radial velocities from the PCRV and RAVE catalogues are different for the subsamples, showing smooth rotations, shears, and deformations of the layer of gas producing stars with the formation of the Gould Belt, the Great Tunnel, the Local Bubble, and other structures within the last 200 Myr. The detected temporal variations of the velocity dispersions, solar motion components, Ogorodnikov-Milne model parameters, and Oort constants are significant, agree with the results of other authors, and show that it is meaningless to calculate the kinematic parameters for samples of stars with uncertain ages or with a wide range of ages.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/158/187
- Title:
- Confirmed members of nearby young moving groups
- Short Name:
- J/AJ/158/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first statistical analysis of exoplanet direct imaging surveys combining adaptive optics (AO) imaging at small separations with deep seeing-limited observations at large separations allowing us to study the entire orbital separation domain from 5 to 5000 au simultaneously. Our sample of 344 stars includes only confirmed members of nearby young associations and is based on all AO direct-imaging detection limits readily available online, with addition of our own previous seeing-limited surveys. Assuming that the companion distribution in mass and a semimajor axis follows a power-law distribution and adding a dependence on the mass of the host star, such as d^2^{prop.to}fM^{alpha}^a^{beta}^(M_*_/M_{sun}_)^{gamma}^dMda, we constrain the parameters to obtain {alpha}=-0.18_-0.65_^+0.77^, {beta}=-1.43_-0.24_^+0.23^, and {gamma}=0.62_-0.50_^+0.56^ at a 68% confidence level, and we obtain f=0.11_-0.05_^+0.11^ for the overall planet occurrence rate for companions with masses between 1 and 20 M_Jup_ in the range of 5-5000 au. Thus, we find that occurrence of companions is negatively correlated with a semimajor axis and companion mass (marginally) but is positively correlated with the stellar host mass. Our inferred mass distribution is in good agreement with other distributions found previously from direct imaging surveys for planets and brown dwarfs, but is shallower as a function of mass than the distributions inferred by radial velocity surveys of gas giants in the 1-3 au range. This may suggest that planets at these wide and very wide separations represent the low-mass tail of the brown dwarfs and stellar companion distribution rather than an extension of the distribution of the inner planets.
- ID:
- ivo://CDS.VizieR/J/AJ/158/87
- Title:
- 86 cool dwarfs observed during K2 Campaigns 1-17
- Short Name:
- J/AJ/158/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present revised stellar properties for 172 K2 target stars that were identified as possible hosts of transiting planets during Campaigns 1-17. Using medium-resolution near-infrared spectra acquired with the NASA Infrared Telescope Facility/SpeX and Palomar/TripleSpec, we found that 86 of our targets were bona fide cool dwarfs, 74 were hotter dwarfs, and 12 were giants. Combining our spectroscopic metallicities with Gaia parallaxes and archival photometry, we derived photometric stellar parameters and compared them to our spectroscopic estimates. Although our spectroscopic and photometric radius and temperature estimates are consistent, our photometric mass estimates are systematically {Delta}M_*_=0.11 M_{sun}_ (34%) higher than our spectroscopic mass estimates for the least massive stars (M_*,phot_<0.4 M_{sun}_). Adopting the photometric parameters and comparing our results to parameters reported in the Ecliptic Plane Input Catalog, our revised stellar radii are {Delta}R_*_=0.15 R_{sun}_ (40%) larger, and our revised stellar effective temperatures are roughly {Delta}T_eff_=65 K cooler. Correctly determining the properties of K2 target stars is essential for characterizing any associated planet candidates, estimating the planet search sensitivity, and calculating planet occurrence rates. Even though Gaia parallaxes have increased the power of photometric surveys, spectroscopic characterization remains essential for determining stellar metallicities and investigating correlations between stellar metallicity and planetary properties.
- ID:
- ivo://CDS.VizieR/J/ApJS/213/5
- Title:
- Cool KOIs. VI. H- and K- band spectra
- Short Name:
- J/ApJS/213/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present H- and K-band spectra for late-type Kepler Objects of Interest (the "Cool KOIs"): low-mass stars with transiting-planet candidates discovered by NASA's Kepler Mission that are listed on the NASA Exoplanet Archive. We acquired spectra of 103 Cool KOIs and used the indices and calibrations of Rojas-Ayala et al. (2012, Cat. J/ApJ/748/93) to determine their spectral types, stellar effective temperatures, and metallicities, significantly augmenting previously published values. We interpolate our measured effective temperatures and metallicities onto evolutionary isochrones to determine stellar masses, radii, luminosities, and distances, assuming the stars have settled onto the main sequence. As a choice of isochrones, we use a new suite of Dartmouth predictions that reliably include mid-to-late M dwarf stars. We identify five M4V stars: KOI-961 (confirmed as Kepler 42), KOI-2704, KOI-2842, KOI-4290, and the secondary component to visual binary KOI-1725, which we call KOI-1725B. We also identify a peculiar star, KOI-3497, which has Na and Ca lines consistent with a dwarf star but CO lines consistent with a giant. Visible-wavelength adaptive optics imaging reveals two objects within a 1 arcsec diameter; however, the objects' colors are peculiar. The spectra and properties presented in this paper serve as a resource for prioritizing follow-up observations and planet validation efforts for the Cool KOIs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/480/2423
- Title:
- CORNISH project IV. Radio-selected galactic PN
- Short Name:
- J/MNRAS/480/2423
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new radio-selected sample of PNe from the CORNISH survey. We find 90 new PNe, of which 12 are newly discovered and 78 are newly classified as PN. A further 47 previously suspected PNe are confirmed as such from the analysis presented here and 24 known PNe are detected. Eight sources are classified as possible PNe or other source types.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A84
- Title:
- Coronae of nearby star clusters
- Short Name:
- J/A+A/645/A84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a novel view on the morphology and dynamical state of ten prominent, nearby (<=500pc), and young (~30-300Myr) open star clusters with Gaia DR2: Per, Blanco 1, IC 2602, IC 2391, Messier 39, NGC 2451A, NGC 2516, NGC 2547, Platais 9, and the Pleiades. We introduce a pioneering member-identification method that is informed by cluster bulk velocities and deconvolves the spatial distribution with a mixture of Gaussians. Our approach enables inferring the true spatial distribution of the clusters by effectively filtering field star contaminants while at the same time mitigating the effect of positional errors along the line of sight. This first application of the method reveals vast stellar coronae that extend for >~100pc and surround the cluster cores, which are comparatively tiny and compact. The coronae and cores form intertwined, coeval, and comoving extended cluster populations, each encompassing tens of thousands of cubic parsec and stretching across tens of degrees on the sky. Our analysis shows that the coronae are gravitationally unbound but largely comprise the bulk of the stellar mass of the populations. Most systems are in a highly dynamic state, showing evidence of expansion and sometimes simultaneous contraction along different spatial axes. The velocity field of the extended populations for the cluster cores appears asymmetric but is aligned along a spatial axis unique to each cluster. The overall spatial distribution and the kinematic signature of the populations are largely consistent with the differential rotation pattern of the Milky Way. This finding underlines the important role of global Galactic dynamics in the fate of stellar systems. Our results highlight the complexity of the Milky Way's open cluster population and call for a new perspective on the characterization and dynamical state of open clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/801/74
- Title:
- Dark matter profiles in dwarf galaxies
- Short Name:
- J/ApJ/801/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gamma-ray searches for dark matter annihilation and decay in dwarf galaxies rely on an understanding of the dark matter density profiles of these systems. Conversely, uncertainties in these density profiles propagate into the derived particle physics limits as systematic errors. In this paper we quantify the expected dark matter signal from 20 Milky Way dwarfs using a uniform analysis of the most recent stellar-kinematic data available. Assuming that the observed stellar populations are equilibrium tracers of spherically symmetric gravitational potentials that are dominated by dark matter, we find that current stellar-kinematic data can predict the amplitudes of annihilation signals to within a factor of a few for the ultra-faint dwarfs of greatest interest. On the other hand, the expected signal from several classical dwarfs (with high-quality observations of large numbers of member stars) can be localized to the ~20% level. These results are important for designing maximally sensitive searches in current and future experiments using space and ground-based instruments.
- ID:
- ivo://CDS.VizieR/J/A+A/577/A81
- Title:
- Deep SDSS Optical Spectroscopy. II.
- Short Name:
- J/A+A/577/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a sample of 3942 low-resolution (R~2000) optical spectra from the Sloan Digital Sky Survey (SDSS), focusing on stars with effective temperatures 5800<Teff<6300K, and distances from the Milky Way plane in excess of 5kpc, and determine their abundances of Fe, Ca, and Mg. This work follows the same methodology as in the previous paper in this series, deriving atmospheric parameters by chi^2^ minimization, but we now obtain the abundances of individual elements by fitting their associated spectral lines. Distances are calculated from absolute magnitudes obtained by a statistical comparison of our stellar parameters with stellar-evolution models. The observations reveal a decrease in the abundances of iron, calcium and magnesium at large distances from the Galactic center. The median abundances for the halo stars analyzed are fairly constant up to a Galactocentric distance r~20kpc, rapidly decrease between r~20 and r~40kpc, and flatten out to significantly lower values at larger distances, consistent with previous studies. In addition, we examine the Ca/Fe and Mg/Fe ratios as a function of Fe/H and Galactocentric distance. Our results show that the most distant parts of the halo show a steeper variation of the Ca/Fe and Mg/Fe with iron. We found that at the range -1.6<[Fe/H]<-0.4 the Ca/Fe ratio decreases with distance, in agreement with earlier results based on local stars. However, the opposite trend is apparent for Mg/Fe. Our conclusion that the outer regions of the halo are more metal-poor than the inner regions, based on in-situ observations of distant stars, is in concert with recent results based on inferences from the kinematics of more local stars, and with predictions of recent galaxy formation simulations for galaxies similar to the Milky Way.
- ID:
- ivo://CDS.VizieR/J/A+A/441/653
- Title:
- 32 DENIS nearby red dwarfs
- Short Name:
- J/A+A/441/653
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectra of 36 nearby star candidates and 3 red giant candidates, identified in the DENIS database. 32 of the dwarf candidates are nearby red dwarfs, with spectral types from M5.5 to M8.5. Out of 11 targets with low proper motion (mu<0.1arcsec/yr) but a Reduced Proper Motion above an inclusive threshold, 9 are red dwarfs. The 4 contaminants are all reddened F-K main sequence stars, and could have been eliminated by checking for small well-known high latitude molecular clouds. These stars might be of interest as probes of interstellar absorption. For the red dwarfs we derive spectral types and spectroscopic distances, using a new calibration of the PC3 spectral index to absolute magnitudes in the I, J, H and K photometric bands. We confirm 2 new members of the 12 pc volume (2 new M8.5), and one M7.5 NLTT object closer than 10pc; and show that one quarter of the stars with photometric distances under 30pc have too small a proper motion for inclusion in the NLTT catalog.
- ID:
- ivo://CDS.VizieR/J/MNRAS/461/839
- Title:
- DIB 661.3nm in Cepheid spectra
- Short Name:
- J/MNRAS/461/839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated the diffuse interstellar band (DIB) at 661.3nm seen in the spectra of Cepheid stars. After removal of the blending lines of ionized yttrium and neutral iron, we determined the equivalent widths (EWs) of the DIB and used these values to investigate the E(B-V)-DIB EW relation. The relation found from Cepheids matches that found in B stars. This relation can help to find the reddening for newly discovered Cepheids without extensive photometric data, and thus determine their distances. The relation between E(B - V) and the DIB EW does not yield precise reddening values. It is not a substitute for better photometric or spectroscopic methods. At best, it is indicative, but it provides some information that may not be otherwise available. Defining R*=E(B-V)/DIB EW, which we consider to be the analogue of R=E(B-V)/A_V_, we investigated the Galactic longitudinal dependence of R* assuming that the DIB EW value is representative of the interstellar absorption A$_v$. We found that there is an apparent increase of the R* value that corresponds to the abnormal absorption seen towards Cygnus constellation. Finally, we constructed a 2D map of the DIB EW distribution in the Galactic disc basing on our rather limited sample of 253 spectra of 176 Cepheids.
