- ID:
- ivo://CDS.VizieR/J/A+A/581/A28
- Title:
- Stellar X-ray flares from the 2XMM catalog
- Short Name:
- J/A+A/581/A28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a uniform, large-scale survey of X-ray flare emission, based on the XMM-Newton Serendipitous Source Catalogue and its associated data products. Our survey comprises both XMM-targeted active stars and those observed serendipitously in the field-of-view of each observation. The 2XMM Catalogue and the associated time-series ('light-curve') data products have been used as the basis for the survey of X-ray flares from cool stars in the Hipparcos Tycho-2 catalogue. Our sample contains ~130 flares with well-observed profiles; they originate from ~70 stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/725/480
- Title:
- Stellar X-ray sources in the COSMOS survey
- Short Name:
- J/ApJ/725/480
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the X-ray properties of a sample of solar- and late-type field stars identified in the Chandra Cosmic Evolution Survey (COSMOS), a deep (160ks) and wide (~0.9deg^2^) extragalactic survey. The sample of 60 sources was identified using both morphological and photometric star/galaxy separation methods. We determine X-ray count rates, extract spectra and light curves, and perform spectral fits to determine fluxes and plasma temperatures. Complementary optical and near-IR photometry is also presented and combined with spectroscopy for 48 of the sources to determine spectral types and distances for the sample. We find distances ranging from 30pc to ~12kpc, including a number of the most distant and highly active stellar X-ray sources ever detected. Overall the sample is typically more luminous than the active Sun, representing the high-luminosity end of the disk and halo X-ray luminosity functions. The halo population appears to include both low-activity spectrally hard sources that may be emitting through thermal bremsstrahlung, as well as a number of highly active sources in close binaries.
- ID:
- ivo://CDS.VizieR/J/MNRAS/451/3693
- Title:
- Stellar yields and the initial mass function
- Short Name:
- J/MNRAS/451/3693
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a set of 144 Galactic chemical evolution models applied to a Milky Way analogue, computed using four sets of low+intermediate star nucleosynthetic yields, six massive star yield compilations, and six functional forms for the initial mass function. A comparison is made between a grid of multiphase chemical evolution models computed with these yield combinations and empirical data drawn from the Milky Way's disc, including the solar neighbourhood. By means of a {chi}^2^ methodology, applied to the results of these multiphase models, the best combination of stellar yields and initial mass function capable of reproducing these observations is identified.
- ID:
- ivo://CDS.VizieR/J/ApJ/857/111
- Title:
- Stellar yields of rotating first stars. II.
- Short Name:
- J/ApJ/857/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent theory predicts that first stars are born with a massive initial mass of >~100M_{sun}_. Pair-instability supernova (PISN) is a common fate for such massive stars. Our final goal is to prove the existence of PISNe and thus the high-mass nature of the initial mass function in the early universe by conducting abundance profiling, in which properties of a hypothetical first star is constrained by metal-poor star abundances. In order to determine reliable and useful abundances, we investigate the PISN nucleosynthesis taking both rotating and nonrotating progenitors for the first time. We show that the initial and CO core mass ranges for PISNe depend on the envelope structures: nonmagnetic rotating models developing inflated envelopes have a lower shifted CO mass range of ~70-125_M{sun}_, while nonrotating and magnetic rotating models with deflated envelopes have a range of ~80-135_M{sun}_. However, we find no significant difference in explosive yields from rotating and nonrotating progenitors, except for large nitrogen production in nonmagnetic rotating models. Furthermore, we conduct the first systematic comparison between theoretical yields and a large sample of metal-poor star abundances. We find that the predicted low [Na/Mg]~-1.5 and high [Ca/Mg]~0.5-1.3 abundance ratios are the most important to discriminate PISN signatures from normal metal-poor star abundances, and confirm that no currently observed metal-poor star matches with the PISN abundance. An extensive discussion on the nondetection is presented.
- ID:
- ivo://CDS.VizieR/J/A+A/593/A123
- Title:
- STELLA-SES Radial Velocities of HD 208472
- Short Name:
- J/A+A/593/A123
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- HD 208472 is among the most active RS CVn binaries with cool starspots. Decade-long photometry had shown that the spots seem to change their longitudinal appearance with a period of about six years, coherent with brightness variations. Our aim is to spatially resolve the stellar surface of HD 208472 and related the photometric results to the true longitudinal and latitudinal spot appearance. Furthermore, we investigate surface differential rotation pattern of the star. We employ three years of high resolution, high S/N spectroscopic data from the STELLA robotic observatory and determine new and more precise stellar physical parameters. Pre-calculated synthetic spectra are fit to each of these spectra and new spot-corrected orbital elements are given. A sample of 34 absorption lines per spectrum is used to calculate mean line profiles with a S/N of several hundred. A total of 13 temperature Doppler images are reconstructed from these line profiles with the inversion code iMap. Differential rotation is investigated by cross-correlating successive Doppler images in each observing season. Spots on HD 208472 are distributed preferably at high latitudes and less occasionally around mid-to-low latitudes. No polar-cap like structure is seen at any epoch. We observed a flip-flop event between 2009 and 2010, manifested as a flip of the spot activity from phase 0.0 to phase 0.5, while the overall brightness of the star continued to increase and reached an all-time maximum in 2014. Cross-correlation of successive Doppler images suggests a solar-like differential rotation which is ~15 times weaker in strength compared to the Sun.
18126. Stephenson H{alpha} stars
- ID:
- ivo://CDS.VizieR/J/A+A/402/963
- Title:
- Stephenson H{alpha} stars
- Short Name:
- J/A+A/402/963
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of spectroscopic observations for 52 objects from the list of H{alpha} emission stars of Stephenson (1986ApJ...300..779S). Out of six known T Tauri stars observed, five showed H{alpha} in emission and in one (StHa 40), H{alpha} changed from being in absorption to emission over a period of two years, accompanied by photometric and spectral type variability. We confirm the T Tauri nature of one Stephenson object (StHa 48) on the basis of the presence of H{alpha} and H{beta} in emission, Li I {lambda}6708 in absorption, infrared excess and X-ray emission. Among the 52 objects observed, there were other emission line objects: 1 Ke star, 1 BQ[] star, 2 galaxies and 2 Be stars. We present a higher-resolution spectrum of StHa 62 showing permitted and forbidden lines in emission typical of BQ[] stars. Twenty five out of 30 newly observed objects failed to show H{alpha} in emission. We also present 2MASS observations for 112 StHa objects. We suggest three Stephenson objects (StHa 52, 125 and 129) to be YSOs on the basis of 2MASS, IRAS and ROSAT observations. These and all other known YSOs amongst StHa stars are found in regions of star-forming clouds in Taurus, Orion and Ophiuchus. YSOs at high galactic latitudes in other parts of the sky are therefore rare.
- ID:
- ivo://CDS.VizieR/J/MNRAS/420/757
- Title:
- STEREO magnetic chemically peculiar stars
- Short Name:
- J/MNRAS/420/757
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- About 10% of upper main-sequence stars are characterized by the presence of chemical peculiarities, often found together with a structured magnetic field. The atmospheres of most of those chemically peculiar stars present surface spots, leading to photometric variability caused by rotational modulation. The study of the light curves of those stars therefore permits a precise measurement of their rotational period, which is important to study stellar evolution and to plan further detailed observations. We analysed the light curves of 1028 chemically peculiar stars obtained with the STEREO spacecraft. We present here the results obtained for the 337 magnetic chemically peculiar stars in our sample.
- ID:
- ivo://CDS.VizieR/J/MNRAS/429/119
- Title:
- STEREO non-magnetic chemically peculiar stars
- Short Name:
- J/MNRAS/429/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analysed the photometric data obtained with the STEREO spacecraft for 558 non-magnetic chemically peculiar (CP) stars to search for rotational and pulsational variability. Applying the Lomb-Scargle and the phase dispersion minimization methods, we have detected photometric variability for 44 objects from which 35 were previously unknown. The new objects are all bright stars on the ecliptic plane (magnitude range 4.7<V<11.7) and will therefore be of great interest to studies of stellar structure and evolution. In particular, several show multiple signals consistent with hybrid {delta} Scuti and {gamma} Doradus pulsation, with different periodicities allowing very different regions of the stellar interior to be studied. There are two subgroups of stars in our sample: the cool metallic line Am (CP1) and the hot HgMn (CP3) stars. These objects fall well inside the classical instability strip where {delta} Scuti, {gamma} Doradus and slowly pulsating B-type stars are located. We also expect to find periods correlated to the orbital period for CP1 objects as they are mostly members of binary systems. For CP3 stars, rotationally induced variability is still a matter of debate. Although surface spots were detected, they are believed to produce only marginal photometric amplitudes. So, periods from several hours to a few days were expected for these two star groups. The STEREO/HI-1 data are well matched to studies of this frequency domain, owing to the cadence of approximately 40-min and multiple epochs over four and a half years. The remaining 514 stars are likely to be constant in the investigated range from 0.1 to 10d. In some cases, the presence of blending or systematic effects prevented us from detecting any reliable variability and in those cases we classified the star as constant. We discuss our results in comparison to already published ones and find a very good agreement. Finally, we have calibrated the variable stars in terms of the effective temperature and luminosity in order to estimate masses and ages. For this purpose, we used specifically developed calibrations for CP stars and, when available, Hipparcos parallaxes. All but two objects cover the stellar mass range from 1.5 to 5M_{sun}_ and are located between the zero- and terminal-age main sequence.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/2477
- Title:
- STEREO observations of variable stars
- Short Name:
- J/MNRAS/416/2477
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The feasibility of using data from the NASA STEREO mission for variable star and asteroseismology studies has been examined. A data analysis pipeline has been developed that is able to apply selected algorithms to the entire database of nearly a million stars to search for signs of variability. An analysis limited to stars of magnitude 10.5 has been carried out, which has resulted in the extraction of 263 eclipsing binaries (EBs), of which 122 are not recorded as such in the SIMBAD online database. The characteristics of the STEREO observations are shown to be extremely well-suited to variable star studies with the ability to provide continuous phase coverage for extended periods as well as repeated visits that allow both short and long term variability to be observed. This will greatly inform studies of particular stars, such as the pre-cataclysmic variable V471 Tau, as well as entire classes of stars, including many forms of rotational variability. The high-precision photometry has also revealed a potentially substellar companion to a bright (R=7.5mag) nearby star (HD 213597), detected with 5 sigma significance. This would provide a significant contribution to exoplanet research if follow-up observations ascertain the mass to be within the planetary domain. Some particularly unusual EBs from the recovered sample are discussed, including a possible reclassification of a well-known star as an EB rather than a rotational variable (HR 7355) and several particularly eccentric systems, including very long-period EBs.
- ID:
- ivo://CDS.VizieR/II/201
- Title:
- Sternberg SN Catalogue, 1994Sep.
- Short Name:
- II/201
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a revised version of "Sternberg Astronomical Institute Supernova Catalogue" which includes data on 930 extragalactic supernovae (SNe) discovered up to September 1, 1994 and the main data on their parent galaxies. The description of previous version was presented by Tsvetkov and Bartunov (1993). The main improvements are the following: 1. The RC3 catalogue (de Vaucouleurs et al., 1991) was used instead of the RC2 as main source of data for parent galaxies. 2. For recent supernovae we included some magnitudes at maximum light from Hamuy et al. (1993) and compared our data with those of van den Bergh (1993). We also corrected some velocities of galaxies according to Huchra et al. (1994). 3. Some galaxy identifications from the MCG ( M ) were replaced by the ones from the PGC and the UGC. The identifications were adopted with this order of preference: NGC (IC) - UGC (ESO) - MCG - PGC - others 4. Photographic magnitudes from the PGC ( marked '*' ) and from IAU circulars ( marked 'C' ) were used when no other data were available. 5. Some errors were found in the previous version, and many new identifications for the galaxies previously listed as "ANON" were adopted. 6. We included several precise astrometric positions of SNe from Porter (1993).