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931. ChIcAGO. I. Sample and initial results
ID:
ivo://CDS.VizieR/J/ApJS/212/13
Title:
ChIcAGO. I. Sample and initial results
Short Name:
J/ApJS/212/13
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the Chasing the Identification of ASCA Galactic Objects (ChIcAGO) survey, which is designed to identify the unknown X-ray sources discovered during the ASCA Galactic Plane Survey (AGPS). Little is known about most of the AGPS sources, especially those that emit primarily in hard X-rays (2-10keV) within the F_x_~10^-13^ to 10^-11^erg/cm2/s X-ray flux range. In ChIcAGO, the subarcsecond localization capabilities of Chandra have been combined with a detailed multiwavelength follow-up program, with the ultimate goal of classifying the >100 unidentified sources in the AGPS. Overall to date, 93 unidentified AGPS sources have been observed with Chandra as part of the ChIcAGO survey. A total of 253 X-ray point sources have been detected in these Chandra observations within 3' of the original ASCA positions. We have identified infrared and optical counterparts to the majority of these sources, using both new observations and catalogs from existing Galactic plane surveys. X-ray and infrared population statistics for the X-ray point sources detected in the Chandra observations reveal that the primary populations of Galactic plane X-ray sources that emit in the F_x_~10^-13^ to 10^-11^ erg/cm2/s flux range are active stellar coronae, massive stars with strong stellar winds that are possibly in colliding wind binaries, X-ray binaries, and magnetars. There is also another primary population that is still unidentified but, on the basis of its X-ray and infrared properties, likely comprises partly Galactic sources and partly active galactic nuclei.
932. Chinese Small Telescope ARray (CSTAR)
ID:
ivo://CDS.VizieR/J/PASP/122/347
Title:
Chinese Small Telescope ARray (CSTAR)
Short Name:
J/PASP/122/347
Date:
21 Oct 2021
Publisher:
CDS
Description:
In 2008 January the twenty-fourth Chinese expedition team successfully deployed the Chinese Small Telescope ARray (CSTAR) to Dome A, the highest point on the Antarctic plateau. CSTAR consists of four 14.5cm optical telescopes, each with a different filter (g,r,i, and open) and has a 4.5{deg}x4.5{deg} field of view (FOV). It operates robotically as part of the Plateau Observatory, PLATO, with each telescope taking an image every ~30s throughout the year whenever it is dark. During 2008, CSTAR 1 performed almost flawlessly, acquiring more than 0.3 million -band images for a total integration time of 1728hr during 158 days of observations. For each image taken under good sky conditions, more than 10,000 sources down to magnitude could be detected. We performed aperture photometry on all the sources in the field to create the catalog described herein. Since CSTAR has a fixed pointing centered on the south celestial pole (Dec=-90{deg}), all the sources within the FOV of CSTAR were monitored continuously for several months. The photometric catalog can be used for studying any variability in these sources, and for the discovery of transient sources such as supernovae, gamma-ray bursts, and minor planets.
933. CHIPS II. O stars in Trumpler 14 CHIPS-Tr14
ID:
ivo://CDS.VizieR/J/A+A/658/A198
Title:
CHIPS II. O stars in Trumpler 14 CHIPS-Tr14
Short Name:
J/A+A/658/A198
Date:
25 Feb 2022 07:07:49
Publisher:
CDS
Description:
Most massive stars belong to multiple systems, yet the formation process leading to such high multiplicity remain insufficiently understood. To help constrain the different formation scenarios that exist, insights on the low-mass end of the companion mass function of such stars is crucial. However, this is a challenging endeavour as (sub-)solar mass companions at angular separations {rho} below 1" (corresponding to 1000-3000au in nearby young open clusters and OB associations) are difficult to detect due to the large brightness contrast with the central star. With the Carina High-contrast Imaging Project of massive Stars (CHIPS), we aim to obtain statistically significant constraints on the presence and properties of low-mass companions around massive stars at a previously unreachable observing window ({Delta}mag>=10 at {rho}<= 1"). In this second paper in the series, we focus on the Trumpler 14 cluster, which harbours some of the youngest and most massive O-type stars in the Milky Way. We obtained VLT-SPHERE observations of seven O-type objects in Trumpler 14 using the IRDIFS_EXT mode. These allow us to search for companions at separations larger than 0.15" (~360au) and down to magnitude contrast >10 mag in the near-infrared. We used angular and spectral differential imaging along with PSF fitting to detect sources and measure their flux relative to that of the central object. We detected 211 sources with near-infrared magnitude contrast in the range of 2 to 12. The closest companion, at only 0.26", is characterised as a 1.4M_{sun}_ stars with an age of 0.6Myr, in excellent agreement with previous age estimates for Tr14. The mass function peaks at about 0.4M_{sun}_ and presents a dearth of stars in the 0.5 to 0.8M_{sun}_ mass range compared to previous estimates of the initial mass function in Tr14.
934. Chromospheric activity of nearby Sun-like stars
ID:
ivo://CDS.VizieR/J/A+A/641/A110
Title:
Chromospheric activity of nearby Sun-like stars
Short Name:
J/A+A/641/A110
Date:
21 Oct 2021
Publisher:
CDS
Description:
The chromospheric emission in the cores of the CaII H & K lines of late-type dwarfs is a well known indicator of magnetic activity that decreases with increasing stellar age. I use this indicator to investigate the formation history of nearby G- and early K-type stars with origins at galactocentric distances similar to that of the region where the Sun was born. A parent sample of single main-sequence stars with near-solar metallicity and known magnetic activity levels is built from catalogues of stellar atmospheric parameters and chromospheric activity indices. A kinematical approach uses Gaia astrometric data to differentiate thin disc stars from thick disc stars. Measured distributions of R'_HK_ chromospheric activity indices are compared with Monte Carlo simulations based on an empirical model of chromospheric activity evolution. The thin disc includes a significant fraction of Sun-like stars with intermediate activity levels while most early K- and G-type stars from the thick disc are inactive. The chromospheric activity distribution among nearby Sun-like dwarfs from the thin disc can be explained by a combination of an old (>6-7Gyr) star formation event (or events) and a more recent (<3Gyr) burst of star formation. Such an event is not required to account for the R'_HK_ index distributions of nearby thick disc stars. The distribution of magnetic activity among local G- and early K-type stars with a near-solar metallicity bears the imprint of an important star formation event that occurred ~1.9 to 2.6Gyr ago in the thin disc of the Milky Way.
935. Chromospheric emission in late-type stars.
ID:
ivo://CDS.VizieR/J/AJ/111/439
Title:
Chromospheric emission in late-type stars.
Short Name:
J/AJ/111/439
Date:
21 Oct 2021
Publisher:
CDS
Description:
More than 800 southern stars within 50pc have been observed for chromospheric emission in the cores of the Ca II H and K lines. Most of the sample targets were selected to be G dwarfs on the basis of colors and spectral types. The bimodal distribution in stellar activity first noted in a sample of northern stars by Vaughan and Preston (1980PASP...92..385V) is confirmed, and the percentage of active stars, about 30%, is remarkably consistent between the northern and southern surveys. This is especially compelling given that we have used an entirely different instrumental setup and stellar sample than used in the previous study. Comparisons to the Sun, a relatively inactive star, show that most nearby solar-type stars have a similar activity level, and presumably a similar age. We identify two additional subsamples of stars -- a very active group, and a very inactive group. The very active group may be made up of young stars near the Sun, accounting for only a few percent of the sample, and appears to be less than ~0.1Gyr old. Included in this high-activity tail of the distribution, however, is a subset of very close binaries of the RS CVn or W UMa types. The remaining members of this population may be undetected close binaries or very young single stars. The very inactive group of stars, contributing ~5%-10% to the total sample, may be those caught during a Maunder Minimum type phase. If the observations of the survey stars are considered to be a sequence of snapshots of the Sun during its life, we might expect that the Sun will spend about 10% of the remainder of its main sequence life in a Maunder Minimum phase.
936. CIG 96 deep optical and HI images
ID:
ivo://CDS.VizieR/J/A+A/619/A163
Title:
CIG 96 deep optical and HI images
Short Name:
J/A+A/619/A163
Date:
21 Oct 2021
Publisher:
CDS
Description:
Asymmetries in atomic hydrogen (HI) in galaxies are often caused by the interaction with close companions, making isolated galaxies an ideal framework to study secular evolution. The AMIGA project has demonstrated that isolated galaxies show the lowest level of asymmetry in their HI integrated profiles compared to even field galaxies, yet some present significant asymmetries. CIG 96 (NGC 864) is a representative case reaching a 16% level. Our aim is to investigate the HI asymmetries of the spiral galaxy CIG 96 and what processes have triggered the star-forming regions observed in the XUV pseudo-ring. We performed deep optical observations at CAHA1.23m, CAHA2.2m and VST (OmegaCAM wide-field camera) telescopes. We reach surface brightness (SB) limits of {mu}_CAHA2.2m_=27.5mag/arcsec^2^ (Cousins R) and {mu}_VST_=28.7mag/arcsec^2^ (SDSS r) that show the XUV pseudo-ring of the galaxy in detail. Additionally, a wavelet filtering of the HI data cube from our deep observations with VLA/EVLA telescope allowed us to reach a column density of N_HI_=8.9x10^18^cm^-2^ (5{sigma}) (28"x28" beam), lower than in any isolated galaxy. We confirm that the HI of CIG 96 extends farther than 4xr_25_ in all directions. Furthermore, we detect for the first time two gaseous structures (~10^6^M_{sun}_) in the outskirts. The SDSS g-r colour index image from CAHA1.23m shows extremely blue colours in certain regions of the pseudo-ring where N_HI_>8.5x10^20^cm^-2^, whereas the rest show red colours. Galactic cirrus contaminate the field, setting an unavoidable detection limit at 28.5mag/arcsec^2^ (SDSS r). At the current SB and NHI levels, we detect no stellar link within 1{deg}x1{deg} or gaseous link within 40'x40' between CIG 96 and any companion. The isolation criteria rule out interactions with other similar-sized galaxies for at least 2.7Gyr. Using existing stellar evolution models, the age of the pseudo-ring is estimated at 1Gyr or older. Undetected previously accreted companions and cold gas accretion remain as the main hypothesis to explain the optical pseudo-ring and HI features of CIG 96.
937. CIG sample 3-dimensional environment
ID:
ivo://CDS.VizieR/J/A+A/564/A94
Title:
CIG sample 3-dimensional environment
Short Name:
J/A+A/564/A94
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the 3-dimensional environment for a sample of 386 galaxies in the Catalogue of Isolated Galaxies (CIG, Karachentseva 1973) using the Ninth Data Release of the Sloan Digital Sky Survey (SDSS-DR9). We aim to identify and quantify the effects of the satellite distribution around a sample of galaxies in the CIG, as well as the effects of the Large Scale Structure (LSS). To recover the physically bound galaxies we first focus on the satellites which are within the escape speed of each CIG galaxy. We also propose a more conservative method using the stacked Gaussian distribution of the velocity difference of the neighbours. The tidal strengths affecting the primary galaxy are estimated to quantify the effects of the local and LSS environments. We also define the projected number density parameter at the fifth nearest neighbour to characterise the LSS around the CIG galaxies. Out of the 386 CIG galaxies considered in this study, at least 340 (88% of the sample) have no physically linked satellite. Following the more conservative Gaussian distribution of physical satellites around the CIG galaxies leads to upper limits. Out of the 386 CIG galaxies, 327 (85% of the sample) have no physical companion within a projected distance of 0.3Mpc. The CIG galaxies are distributed following the LSS of the local Universe, although presenting a large heterogeneity in their degree of connection with it. When present around a CIG galaxy, the effect of physically bound galaxies largely dominates (usually by more than 90%) the tidal strengths generated by the LSS. The CIG samples a variety of environments, from galaxies with physical satellites to galaxies with no neighbours within 3Mpc. A clear segregation appears between early-type CIG galaxies with companions and isolated late-type CIG galaxies. Isolated galaxies are in general bluer, with likely younger stellar populations and rather high star formation with respect to older, redder CIG galaxies with companions. Reciprocally, the satellites are redder and with an older stellar populations around massive early-type CIG galaxies, while they have a younger stellar content around massive late-type CIG galaxies. This suggests that the CIG is composed of a heterogeneous population of galaxies, sampling from old to more recent, dynamical systems of galaxies. CIG galaxies with companions might have a mild tendency (0.3-0.4dex) to be more massive, and may indicate a higher frequency of having suffered a merger in the past.
938. [CII] emission in the ISM of 20 nearby galaxies
ID:
ivo://CDS.VizieR/J/ApJ/845/96
Title:
[CII] emission in the ISM of 20 nearby galaxies
Short Name:
J/ApJ/845/96
Date:
21 Oct 2021
Publisher:
CDS
Description:
The [CII]158{mu}m fine-structure line is the brightest emission line observed in local star-forming galaxies. As a major coolant of the gas-phase interstellar medium, [CII] balances the heating, including that due to far- ultraviolet photons, which heat the gas via the photoelectric effect. However, the origin of [CII] emission remains unclear because C+ can be found in multiple phases of the interstellar medium. Here we measure the fractions of [CII] emission originating in the ionized and neutral gas phases of a sample of nearby galaxies. We use the [NII]205{mu}m fine-structure line to trace the ionized medium, thereby eliminating the strong density dependence that exists in the ratio of [CII]/[NII]122{mu}m. Using the FIR [CII] and [NII] emission detected by the KINGFISH (Key Insights on Nearby Galaxies: a Far- Infrared Survey with Herschel) and Beyond the Peak Herschel programs, we show that 60%-80% of [CII] emission originates from neutral gas. We find that the fraction of [CII] originating in the neutral medium has a weak dependence on dust temperature and the surface density of star formation, and has a stronger dependence on the gas-phase metallicity. In metal-rich environments, the relatively cooler ionized gas makes substantially larger contributions to total [CII] emission than at low abundance, contrary to prior expectations. Approximate calibrations of this metallicity trend are provided.
939. Circumstellar discs at white dwarfs
ID:
ivo://CDS.VizieR/J/MNRAS/449/574
Title:
Circumstellar discs at white dwarfs
Short Name:
J/MNRAS/449/574
Date:
21 Oct 2021
Publisher:
CDS
Description:
White dwarfs whose atmospheres are polluted by terrestrial-like planetary debris have become a powerful and unique tool to study evolved planetary systems. This paper presents results for an unbiased Spitzer Infrared Array Camera search for circumstellar dust orbiting a homogeneous and well-defined sample of 134 single white dwarfs. The stars were selected without regard to atmospheric metal content but were chosen to have (1) hydrogen-rich atmospheres, (2) 17000<Teff<25000K and correspondingly young post-main-sequence ages of 15-270Myr, and (3) sufficient far-ultraviolet brightness for a corresponding Hubble Space Telescope COS snapshot. Five white dwarfs were found to host an infrared bright dust disc, three previously known, and two reported here for the first time, yielding a nominal 3.7^+2.4^_-1.0_ percent of white dwarfs in this post-main-sequence age range with detectable circumstellar dust. Remarkably, the complementary Hubble observations indicate that a fraction of 27 percent show metals in their photosphere that can only be explained with ongoing accretion from circumstellar material, indicating that nearly 90 percent of discs escape detection in the infrared, likely due to small emitting surface area. This paper also presents the distribution of disc fractional luminosity as a function of cooling age for all known dusty white dwarfs, suggesting possible disc evolution scenarios and indicating an undetected population of circumstellar discs.
940. Circumstellar disk candidates in Orion
ID:
ivo://CDS.VizieR/J/AJ/119/3026
Title:
Circumstellar disk candidates in Orion
Short Name:
J/AJ/119/3026
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an optical study of four 45'x45' fields centered ~0.5{deg} east, west, north, and south of the Orion Nebula Cluster center. We have measured V and I_C_ photometry for ~5000 stars, and U photometry for ~1600 of these. We have obtained spectral classifications for ~300 of the stars with UVI_C_ photometry plus an additional ~200 stars located outside the area of our photometric survey. Dereddened photometry allows us to investigate the evidence for circumstellar accretion disks from excess emission at ultraviolet wavelengths, as well as the mass and age distributions of our sample. We find ~230 active accretion disk candidates and estimate the accretion disk fraction at >~40%. We use the magnitude of the ultraviolet excess to infer disk accretion rates. The mass accretion rate (dM/dt) decreases slowly with age over the limited age range spanned by our data, 1-3Myr, and increases slowly with mass over the limited mass range 0.2-1.2 M_{sun}_.