- ID:
- ivo://CDS.VizieR/J/ApJ/864/11
- Title:
- The VVV Variables (V^4^) catalog
- Short Name:
- J/ApJ/864/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Time-varying phenomena are one of the most substantial sources of astrophysical information, and their study has led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search for and analyze variable sources in the near-infrared Ks band using the data from the VISTA Variables in the Via Lactea (VVV) ESO Public Large Survey. This process relies on the characterization of variable sources using different variability indices calculated from time series generated with point-spread function (PSF) photometry of sources under analysis. In particular, we used two main indices, the total amplitude {Delta}Ks and the eta index {eta}, to identify variable sources. Once the variable objects are identified, periods are determined with generalized Lomb-Scargle periodograms and the information potential metric. Variability classes are assigned according to a compromise between comparisons with VVV templates and the period of the variability. The automated tool is applied on VVV tiles d001 and d002 and led to the discovery of 200 variable sources. We detected 70 irregular variable sources and 130 periodic ones. In addition, nine open-cluster candidates projected in the region are analyzed, and the infrared variable candidates found around these clusters are further scrutinized by cross-matching their locations against emission star candidates from VPHAS+ survey H{alpha} color cuts.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/212/1
- Title:
- The WISE catalog of Galactic HII regions
- Short Name:
- J/ApJS/212/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using data from the all-sky Wide-Field Infrared Survey Explorer (WISE) satellite, we made a catalog of over 8000 Galactic HII regions and HII region candidates by searching for their characteristic mid-infrared (MIR) morphology. WISE has sufficient sensitivity to detect the MIR emission from H II regions located anywhere in the Galactic disk. We believe this is the most complete catalog yet of regions forming massive stars in the Milky Way. Of the ~8000 cataloged sources, ~1500 have measured radio recombination line (RRL) or H{alpha} emission, and are thus known to be H II regions. This sample improves on previous efforts by resolving H II region complexes into multiple sources and by removing duplicate entries. There are ~2500 candidate H II regions in the catalog that are spatially coincident with radio continuum emission. Our group's previous RRL studies show that ~95% of such targets are H II regions. We find that ~500 of these candidates are also positionally associated with known H II region complexes, so the probability of their being bona fide H II regions is even higher. At the sensitivity limits of existing surveys, ~4000 catalog sources show no radio continuum emission. Using data from the literature, we find distances for ~1500 catalog sources, and molecular velocities for ~1500H II region candidates.
- ID:
- ivo://CDS.VizieR/J/AJ/109/1095
- Title:
- Thick Disk Chemical Abundance Distribution
- Short Name:
- J/AJ/109/1095
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a determination of the thick disk iron abundance distribution obtained from an in situ sample of F/G stars. These stars are faint, 15<=V=<18, selected on the basis of color, being a subset of the larger survey of Gilmore and Wyse designed to determine the properties of the stellar populations several kiloparsecs from the Sun. The fields studied in the present paper probe the iron abundance distribution of the stellar populations of the galaxy at 500-3000pc above the plane, at the solar Galactocentric distance. The derived chemical abundance distributions are consistent with no metallicity gradients in the thick disk over this range of vertical distance, and with an iron abundance distribution for the thick disk that has a peak at -0.7dex. The lack of a vertical gradient argues against slow, dissipational settling as a mechanism for the formation of the thick disk. The photometric and metallicity data support a turn-off of the thick disk that is comparable in age to the metal-rich globular clusters, or >=12Gyr, and are consistent with a spread to older ages.
- ID:
- ivo://CDS.VizieR/J/PAZh/38/860
- Title:
- Thin disk BV-GV Hipparcos stars within 333pc
- Short Name:
- J/PAZh/38/860
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The variations of kinematic parameters with age are considered for a sample of 15402 thin-disk O-F stars with accurate RA, DEC, proper motion, and parallax higher than 3 mas from the Hipparcos catalogue (2007A&A...474..653V) and radial velocities from the PCRV (2006PAZh...32..844G) catalogue. The ages have been calculated from the positions of the stars on the Hertzsprung-Russell diagram relative to the isochrones from the Padova database (http://stev.oapd.inaf.it/cmd) by taking into account the extinction from the previously constructed 3D analytical model (2009AstL...35..780G) and extinction coefficient RV from the 3D map of its variations (2012AstL...38...12G). Smooth, mutually reconciled variations of the velocity dispersions sigma(U), sigma(V), sigma(W), solar motion components Usun, Vsun, Wsun, Ogorodnikov-Milne model parameters, Oort constants, and vertex deviation lxy consistent with all of the extraneous results for which the stellar ages were determined have been found and presented in the table solution.dat. The velocity dispersion variations are well fitted by power laws the deviations from which are explained by the influence of predominantly radial stellar streams: Sirius, Hyades, alpha Cet/Wolf 630, and Hercules. The accuracy of determining the solar motion relative to the local standard of rest is shown to be fundamentally limited due to these variations of stellar kinematics. The deviations of our results from those of Dehnen and Binney (1998MNRAS.294..429D), the Geneva-Copenhagen survey of dwarfs (V/117), and the Besancon model of the Galaxy (2003A&A...409..523R) are explained by the use of PCRV radial velocities with corrected systematic errors.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/1468
- Title:
- Transient black hole X-ray binaries XMM obs.
- Short Name:
- J/MNRAS/471/1468
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- All observations of Galactic X-ray binaries are affected by absorption from gas and dust in the interstellar medium (ISM) which imprints narrow (line) and broad (photoelectric edges) features on the continuum emission spectrum of the binary. Any spectral model used to fit data from a Galactic X-ray binary must therefore take account of these features; when the absorption is strong (as for most Galactic sources) it becomes important to accurately model the ISM absorption in order to obtain unbiased estimates of the parameters of the (emission) spectrum of the binary system. In this paper, we present analysis of some of the best spectroscopic data from the XMM-Newton RGS instrument using the most up-to-date photoabsorption model of the gaseous ISM ISMabs. We calculate column densities for H, O, Ne and Fe for seven transient black hole X-ray binary systems. We find that the hydrogen column densities in particular can vary greatly from those presented elsewhere in the literature. We assess the impact of using inaccurate column densities and older X-ray absorption models on spectral analysis using simulated data. We find that poor treatment of absorption can lead to large biases in inferred disc properties and that an independent analysis of absorption parameters can be used to alleviate such issues.
- ID:
- ivo://CDS.VizieR/J/AJ/154/115
- Title:
- Travel times of stars within about 300 lt-yr
- Short Name:
- J/AJ/154/115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New means of interstellar travel are now being considered by various research teams, assuming lightweight spaceships to be accelerated via either laser or solar radiation to a significant fraction of the speed of light (c). We recently showed that gravitational assists can be combined with the stellar photon pressure to decelerate an incoming lightsail from Earth and fling it around a star or bring it to rest. Here, we demonstrate that photogravitational assists are more effective when the star is used as a bumper (i.e., the sail passes "in front of" the star) rather than as a catapult (i.e., the sail passes "behind" or "around" the star). This increases the maximum deceleration at {alpha} Cen A and B and reduces the travel time of a nominal graphene-class sail (mass-to-surface ratio 8.6*10^-4^g/m^2^) from 95 to 75 years. The maximum possible velocity reduction upon arrival depends on the required deflection angle from {alpha} Cen A to B and therefore on the binary's orbital phase. Here, we calculate the variation of the minimum travel times from Earth into a bound orbit around Proxima for the next 300 years and then extend our calculations to roughly 22000 stars within about 300lt-yr. Although {alpha} Cen is the most nearby star system, we find that Sirius A offers the shortest possible travel times into a bound orbit: 69 years assuming 12.5% c can be obtained at departure from the solar system. Sirius A thus offers the opportunity of flyby exploration plus deceleration into a bound orbit of the companion white dwarf after relatively short times of interstellar travel.
- ID:
- ivo://CDS.VizieR/J/ApJ/893/56
- Title:
- T Tauri star IR excesses & Ha eq. widths
- Short Name:
- J/ApJ/893/56
- Date:
- 19 Jan 2022 11:42:19
- Publisher:
- CDS
- Description:
- We present a study of the evolution of the inner few astronomical units of protoplanetary disks around low-mass stars. We consider nearby stellar groups with ages spanning from 1 to 11Myr, distributed into four age bins. Combining PANSTARSS photometry with spectral types, we derive the reddening consistently for each star, which we use (1) to measure the excess emission above the photosphere with a new indicator of IR excess and (2) to estimate the mass accretion rate (dM/dt) from the equivalent width of the H{alpha} line. Using the observed decay of dM/dt as a constraint to fix the initial conditions and the viscosity parameter of viscous evolutionary models, we use approximate Bayesian modeling to infer the dust properties that produce the observed decrease of the IR excess with age, in the range between 4.5 and 24{mu}m. We calculate an extensive grid of irradiated disk models with a two-layered wall to emulate a curved dust inner edge and obtain the vertical structure consistent with the surface density predicted by viscous evolution. We find that the median dust depletion in the disk upper layers is {epsilon}~3x10^-3^ at 1.5Myr, consistent with previous studies, and it decreases to {epsilon}~3x10^-4^ by 7.5Myr. We include photoevaporation in a simple model of the disk evolution and find that a photoevaporative wind mass-loss rate of ~1-3x10^-9^M_{sun}_/yr agrees with the decrease of the disk fraction with age reasonably well. The models show the inward evolution of the H_2_O and CO snowlines.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/527
- Title:
- Tully-Fisher distances for Spitzer galaxies
- Short Name:
- J/MNRAS/444/527
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper involves a data release of the observational campaign: Cosmicflows with Spitzer (CFS). Surface photometry of the 1270 galaxies constituting the survey is presented. An additional ~400 galaxies from various other Spitzer surveys are also analysed. CFS complements the Spitzer Survey of Stellar Structure in Galaxies, that provides photometry for an additional 2352 galaxies, by extending observations to low galactic latitudes (|b|<30{deg}). Among these galaxies are calibrators, selected in the K band, of the Tully-Fisher relation. The addition of new calibrators demonstrates the robustness of the previously released calibration. Our estimate of the Hubble constant using supernova host galaxies is unchanged, H_0_=75.2+/-3.3km/s/Mpc. Distance-derived radial peculiar velocities, for the 1935 galaxies with all the available parameters, will be incorporated into a new data release of the Cosmicflows project. The size of the previous catalogue will be increased by 20 percent, including spatial regions close to the Zone of Avoidance.
- ID:
- ivo://CDS.VizieR/J/AJ/159/105
- Title:
- Two new stellar associations in vicinity of the Sun
- Short Name:
- J/AJ/159/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this work we report the discovery of two new stellar associations in close vicinity of the Sun at roughly 180 and 150pc. These two associations, u-Tau assoc and e-Tau assoc, were detected based on their clustering in a multi-dimensional parameter space including {alpha}, {delta}, {mu}_{alpha}_, {mu}_{delta}_, and \bar{omega} of Gaia. The fitting of pre-main-sequence model isochrones in their color-magnitude diagrams suggests that the two associations are of about 50Myr old and the group members lower than ~0.8M_{sun}_ are at the stage of post-T Tauri.
- ID:
- ivo://CDS.VizieR/J/PAZh/37/769
- Title:
- Tycho-2 red giant branch and carbon stars
- Short Name:
- J/PAZh/37/769
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on multicolor photometry from the 2MASS and Tycho-2 catalogues, we have produced a sample of 38368 branch red giants that has less than 1% of admixtures and is complete within 500 pc of the Sun. The sample includes 30671 K giants, 7544 M giants,49 C giants, and 104 suspected supergiants or S stars. The photometric distances have been calculated for K, M, and C stars with an accuracy of 40% together with reddening and extinction estimates. Tycho-2 proper motions and PCRV radial velocities are used to analyze the stellar kinematics. The majority of the selected K and M giants are disk stars with ages of more than 3Gyr. A small number of K and M giants are extremely young or, conversely, thick-disk ones. The spatial distribution and kinematics of the selected C stars force us to consider them as asymptotic branch giants with masses of more than 2 solar masses and ages of less than 2Gyr probably associated with the Gould Belt. The offset of the Sun above the Galactic equator has been found from the distribution of stars to be 13+/-2pc, which coincides with the previously obtained value for the clump red giants.
