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- ID:
- ivo://CDS.VizieR/J/PASJ/53/517
- Title:
- Water maser survey of late-type stars
- Short Name:
- J/PASJ/53/517
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents new results of a water maser survey of late-type stellar objects at 22.235GHz with the Kashima 34-m radio telescope. We have detected 179 out of 643 observed sources, including 32 new detections. The sources were selected in terms of the IRAS flux density and colors of late-type stars, involving optically observable Mira/semi-regular variables, IRC objects, OH/IR sources and proto-planetary nebulae. We found the highest H_2_O detection rate for the type of stars with a thin dust envelope (Mira/semi-regular variables) among other types of sources. This is attributed to the smaller distances to such stars in the sample. The velocity spread of the H_2_O maser profile has an increasing tendency with the IRAS color, though it becomes more difficult to access this color dependence beyond an edge of the transition of the (oxygen-rich) Asymptotic Giant Branch stars to protoplanetary nebulae in the two-color diagram.
- ID:
- ivo://CDS.VizieR/J/A+A/587/A42
- Title:
- weak G-band stars abundances
- Short Name:
- J/A+A/587/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Weak G-band (wGb) stars are a very peculiar class of red giants; they are almost devoided of carbon and often present mild lithium enrichment. Despite their very puzzling abundance patterns, very few detailed spectroscopic studies existed up to a few years ago, which prevented any clear understanding of the wGb phenomenon. We recently proposed the first consistent analysis of published data for a sample of 28 wGb stars and were able to identify them as descendants of early A-type to late B-type stars, although we were not able to conclude on their evolutionary status or the origin of their peculiar abundance pattern. Using new high-resolution spectra, we present the study of a new sample of wGb stars with the aim of homogeneously deriving their fundamental parameters and surface abundances for a selected set of chemical species that we use to improve our insight on this peculiar class of objects. We obtained high-resolution and high signal-to-noise spectra for 19 wGb stars in the southern and northern hemisphere that we used to perform consistent spectral synthesis to derive their fundamental parameters and metallicities, as well as the spectroscopic abundances for Li, C, ^12^C/^13^C, N, O, Na, Sr, and Ba. We also computed dedicated stellar evolution models that we used to determine the masses and to investigate the evolutionary status and chemical history of the stars in our sample. We confirm that the wGb stars are stars with initial masses in the range 3.2 to 4.2M_{sun}_. We suggest that a large fraction could be mildly evolved stars on the subgiant branch currently undergoing the first dredge-up, while a smaller number of stars are more probably in the core He burning phase at the clump. After analysing their abundance pattern, we confirm their strong nitrogen enrichment anti-correlated with large carbon depletion, characteristic of material fully processed through the CNO cycle to an extent not known in evolved intermediate-mass stars in the field and in open clusters. However, we demonstrate here that such a pattern is very unlikely owing to self-enrichment. In the light of the current observational constraints, no solid self-consistent pollution scenario can be presented either, leaving the wGb puzzle largely unsolved.
- ID:
- ivo://CDS.VizieR/J/A+A/401/997
- Title:
- Wilson-Bappu relation in late-type stars
- Short Name:
- J/A+A/401/997
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Wilson & Bappu (1957ApJ...125..661W) have shown the existence of a remarkable correlation between the width of the emission in the core of the K line of CaII and the absolute visual magnitude of late-type stars. Here we present a new calibration of the Wilson-Bappu effect based on a sample of 119 nearby stars. We use, for the first time, width measurements based on high resolution and high signal to noise ratio CCD spectra and absolute visual magnitudes from the Hipparcos database.
- ID:
- ivo://CDS.VizieR/J/ApJS/181/444
- Title:
- X-emitting stars identified from the RASS/SDSS
- Short Name:
- J/ApJS/181/444
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ROSAT All-Sky Survey (RASS) was the first imaging X-ray survey of the entire sky. Combining the RASS Bright and Faint Source Catalogs (Cat. <IX/10>, 1RXS and <IX/29>) yields an average of about three X-ray sources per square degree. However, while X-ray source counterparts are known to range from distant quasars to nearby M dwarfs, the RASS data alone are often insufficient to determine the nature of an X-ray source. As a result, large-scale follow-up programs are required to construct samples of known X-ray emitters. We use optical data produced by the Sloan Digital Sky Survey (SDSS) to identify 709 stellar X-ray emitters cataloged in the RASS and falling within the SDSS Data Release 1 footprint. Most of these are bright stars with coronal X-ray emission unsuitable for SDSS spectroscopy, which is designed for fainter objects (g>15[mag]). Instead, we use SDSS photometry, correlations with the Two Micron All Sky Survey and other catalogs, and spectroscopy from the Apache Point Observatory 3.5m telescope to identify these stellar X-ray counterparts. Our sample of 707 X-ray-emitting F, G, K, and M stars is one of the largest X-ray-selected samples of such stars. We identify 17 new X-ray-emitting DA (hydrogen) WDs, of which three are newly identified WDs. We report on follow-up observations of three candidate cool X-ray-emitting WDs (one DA and two DB (helium) WDs); we have not confirmed X-ray emission from these WDs.
- ID:
- ivo://CDS.VizieR/J/A+A/461/669
- Title:
- XMM observations of Cha I dark cloud
- Short Name:
- J/A+A/461/669
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-mass stars are known to exhibit strong X-ray emission during the early stages of evolution. Nearby star forming regions are ideal targets to study the X-ray properties of pre-main sequence stars. Aims. A deep XMM-Newton exposure is used to investigate X-ray properties of the pre-main sequence population of the Chamaeleon I star forming region. The northern-eastern fringe of the Chameleon I dark cloud was observed with XMM-Newton, revisiting a region observed with ROSAT 15 years ago. Centered on the extended X-ray source CHXR 49 we are able to resolve it into three major contributing components and to analyse their spectral properties. Furthermore, the deep exposure allows not only the detection of numerous, previously unknown X-ray sources, but also the investigation of variability and the study of the X-ray properties for the brighter targets in the field. We use EPIC spectra, to determine X-ray brightness, coronal temperatures and emission measures for these sources, compare the properties of classical and weak-line T Tauri stars and make a comparison with results from the ROSAT observation.
- ID:
- ivo://CDS.VizieR/J/A+A/456/977
- Title:
- XMM observations of NGC 2516 stars
- Short Name:
- J/A+A/456/977
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the characteristics of the X-ray variability of stars in the cluster NGC 2516 as derived from XMM-Newton/EPIC/pn data. The X-ray variations on short (hours), medium (months), and long (years) time scales have been explored. We detected 303 distinct X-ray sources by analysing six EPIC/pn observations; 194 of them are members of the cluster. Stars of all spectral types, from the early-types to the late-M dwarfs, were detected.
- ID:
- ivo://CDS.VizieR/J/other/RAA/19.98
- Title:
- X-ray activity from different types of stars
- Short Name:
- J/other/RAA/19.9
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray emission is an important indicator of stellar activity. In this paper, we study stellar X-ray activity using the XMM-Newton and LAMOST data for different types of stars. We provide a sample including 1259 X-ray-emitting stars, of which 1090 have accurate stellar parameter estimations. Our sample size is much larger than those used in previous works. We find a bimodal distribution of the X-ray to optical flux ratio (log(fX/fV)) for G and K stars. We interpret that this bimodality is due to two subpopulations with different coronal heating rates. Furthermore, using the full widths at half maxima calculated from H{alpha} and H{beta} lines, we show that these stars in the inactive peaks have smaller rotational velocities. This is consistent with the magnetic dynamo theory that presumes stars with low rotational velocities have low levels of stellar activity. We also examine the correlation between log(fX/fV) and luminosity of the excess emission in the H{alpha} line, and find a tight relation between the coronal and chromospheric activity indicators.
- ID:
- ivo://CDS.VizieR/J/MNRAS/422/2024
- Title:
- X-ray-age relation and exoplanet evaporation
- Short Name:
- J/MNRAS/422/2024
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the relationship between coronal X-ray emission and stellar age for late-type stars, and the variation of this relationship with spectral type. We select 717 stars from 13 open clusters and find that the ratio of X-ray to bolometric luminosity during the saturated phase of coronal emission decreases from 10^-3.1^ for late K-dwarfs to 10^-4.3^ for early F-type stars (across the range 0.29<(B-V)_0_<1.41). Our determined saturation timescales vary between 10^7.6^ and 10^8.3^ years, though with no clear trend across the whole FGK range. We apply our X-ray emission - age relations to the investigation of the evaporation history of 121 known transiting exoplanets using a simple energy -limited model of evaporation and taking into consideration Roche lobe effects and different heating/evaporation efficiencies. We confirm that a linear cut-off of the planet distribution in the M^2^/R^3^ versus a^-2^ plane is an expected result of population modification by evaporation and that the known transiting exoplanets display such a cut-off. We find that for an evaporation efficiency of 25 percent we expect around 1 in 5 of the known transiting exoplanets to have lost >10 percent of their mass since formation. In addition we provide estimates of the minimum formation mass for which a planet could be expected to survive for 4Gyrs for a range of stellar and planetary parameters. We emphasise the importance of the earliest periods of a planet's life for its evaporation history with 75 percent expect to occur within the first Gyr. This raises the possibility of using evaporation histories to distinguish different migration mechanisms. For planets with spin-orbit angles available from measurements of the Rossiter-McLaughlin effect no difference is found between the distributions of planets with misaligned orbits and those with aligned orbits. This suggests that dynamical effects accounting for misalignment occur early in the life of a planetary system, although additional data is required to test this.
- ID:
- ivo://CDS.VizieR/J/ApJ/414/846
- Title:
- X-ray emission at the low-mass end
- Short Name:
- J/ApJ/414/846
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have used all tha available data from the Einstein Observatory Imaging Proportional Counter (IPC), and a critical compilation of catalogued optical data, to measure the 0.16-3.5 keV X-ray emission from 88 K and 169 M stars of luminosity classes IV, V and VI within 25 pc from the Sun. The IPC detected 54 out of the 88 K stars, 70 out of the 138 M stars with M_v_ less than 13.4 (corresponding approximatively to M5), and 15 out of the 31 fainter M stars. We have identified a subsample of surveyed stars that is statistically representative of the population of K and M stars in the solar neighborhood.
