- ID:
- ivo://CDS.VizieR/J/A+A/598/A116
- Title:
- A grid of 1D low-mass star formation models
- Short Name:
- J/A+A/598/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Numerical simulations of star formation are becoming ever more sophisticated, incorporating new physical processes in increasingly realistic set-ups. These models are being compared to the latest observations through state-of-the-art synthetic renderings that trace the different chemical species present in the protostellar systems. The chemical evolution of the interstellar and protostellar matter is very topical, with more and more chemical databases and reaction solvers available online to the community. The current study was developed to provide a database of relatively simple numerical simulations of protostellar collapse as a template library for observations of cores and very young protostars, and for researchers who wish to test their chemical modelling under dynamic astrophysical conditions. It was also designed to identify statistical trends that may appear when running many models of the formation of low-mass stars by varying the initial conditions. A large set of 143 calculations of the gravitational collapse of an isolated sphere of gas with uniform temperature and a Bonnor-Ebert-like density profile was undertaken using a 1D fully implicit Lagrangian radiation hydrodynamics code. The parameter space covered initial masses from 0.2 to 8M_{sun}_, temperatures of 5-30K, and radii 3000-30,000AU. A spread due to differing initial conditions and optical depths, was found in the thermal evolutionary tracks of the runs. Within less than an order of magnitude, all first and second Larson cores had masses and radii essentially independent of the initial conditions. Radial profiles of the gas density, velocity, and temperature were found to vary much more outside of the first core than inside. The time elapsed between the formation of the first and second cores was found to strongly depend on the first core mass accretion rate, and no first core in our grid of models lived for longer than 2000 years before the onset of the second collapse. The end product of a protostellar cloud collapse, the second Larson core, is at birth a canonical object with a mass and radius of about 3M_jup_ and 8R_jup_, independent of its initial conditions. The evolution sequence which brings the gas to stellar densities can, however, proceed in a variety of scenarios, on different timescales or along different isentropes, but each story line can largely be predicted by the initial conditions.
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- ID:
- ivo://CDS.VizieR/J/A+A/601/A10
- Title:
- A grid of MARCS model atmospheres for S stars
- Short Name:
- J/A+A/601/A10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- S-type stars are late-type giants whose atmospheres are enriched in carbon and s-process elements because of either extrinsic pollution by a binary companion or intrinsic nucleosynthesis and dredge-up on the thermally-pulsing asymptotic giant branch. A grid of MARCS model atmospheres has been computed for S stars, covering the range 2700<=Teff(K)<=4000, 0.50<=C/O<0.99, 0<=logg<=5, [Fe/H]=0., -0.5dex, and [s/Fe]= 0, 1, and 2 dex (where the latter quantity refers to the global overabundance of s-process elements). The MARCS models make use of a new ZrO line list. Synthetic spectra computed from these models are used to derive photometric indices in the Johnson and Geneva systems, as well as TiO and ZrO band strengths. A method is proposed to select the model best matching any given S star, a non-trivial operation since the grid contains more than 3500 models covering a five-dimensional parameter space. The method is based on the comparison between observed and synthetic photometric indices and spectral band strengths, and has been applied on a vast subsample of the Henize sample of S stars. Our results confirm the old claim by Piccirillo (1980MNRAS.190..441P) that ZrO bands in warm S stars (Teff > 3200K) are not caused by the C/O ratio being close to unity, as traditionally believed, but rather by some Zr overabundance. The TiO and ZrO band strengths, combined with V-K and J-K photometric indices, are used to select Teff, C/O, [Fe/H] and [s/Fe]. The Geneva U-B_1 and B_2-V_1 indices (or any equivalent) are good at selecting the gravity. The defining spectral features of dwarf S stars are outlined, but none is found among the Henize S stars. More generally, it is found that, at Teff=3200K, a change of C/O from 0.5 to 0.99 has a strong impact on V-K (2mag). Conversely, a range of 2 mag in V-K corresponds to a 200K shift along the (Teff, V-K) relationship (for a fixed C/O value). Hence, the use of a (Teff, V-K) calibration established for M stars will yield large errors for S stars, so that a specific calibration must be used, as provided in the present paper. Using the atmospheric parameters derived by our method for the sample of Henize S stars, we show that the extrinsic-intrinsic dichotomy among S stars reveals itself very clearly as a bimodal distribution in the effective temperatures. Moreover, the increase of s-process element abundances with increasing C/O ratios and decreasing temperatures is apparent among intrinsic stars, confirming theoretical expectations.
703. A-G star metallicity
- ID:
- ivo://CDS.VizieR/J/MNRAS/320/451
- Title:
- A-G star metallicity
- Short Name:
- J/MNRAS/320/451
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Edinburgh-Cape Blue Object Survey is an ongoing project to identify and analyse a large sample of hot stars selected initially on the basis of photographic colours (down to a magnitude limit (B~18.0) over the entire high-Galactic-latitude southern sky, and then studied with broad-band UBV photometry and medium-resolution spectroscopy. Due to unavoidable errors in the initial candidate selection, stars that are likely metal-deficient dwarfs and giants of the halo and thick-disc populations are inadvertently included, yet are of interest in their own right. In this paper we discuss a total of 206 candidate metal-deficient dwarfs, subgiants, giants, and horizontal-branch stars with photoelectric colours redder than (B-V)_0_=0.3, and with available spectroscopy. Radial velocities, accurate to ~10-15km/s, are presented for all of these stars. Spectroscopic metallicity estimates for these stars are obtained using a recently recalibrated relation between Ca II K-line strength and (B-V)_0_ colour. The identification of metal-poor stars from this colour-selection technique is remarkably efficient, and competitive with previous survey methods. An additional sample of 186 EC stars with photoelectric colours in the range -0.4<=(B-V)_0_<0.3, photoelectric colours in the range composed primarily of field horizontal-branch stars and other, higher gravity, A- and B-type stars, is also analysed. Estimates of the physical parameters T_eff_, log g and [Fe/H] are obtained for cooler members of this subsample, and a number of candidate RR Lyrae variables are identified.
- ID:
- ivo://CDS.VizieR/J/MNRAS/507/1847
- Title:
- A HARPS-N mass for the elusive Kepler-37d
- Short Name:
- J/MNRAS/507/1847
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To date, only 18 exoplanets with radial velocity (RV) semi-amplitudes <2m/s have had their masses directly constrained. The biggest obstacle to RV detection of such exoplanets is variability intrinsic to stars themselves, e.g. nuisance signals arising from surface magnetic activity such as rotating spots and plages, which can drown out or even mimic planetary RV signals. We use Kepler-37 - known to host three transiting planets, one of which, Kepler-37d, should be on the cusp of RV detectability with modern spectrographs - as a case study in disentangling planetary and stellar activity signals. We show how two different statistical techniques - one seeking to identify activity signals in stellar spectra, and another to model activity signals in extracted RVs and activity indicators - can enable detection of the hitherto elusive Kepler-37d. Moreover, we show that these two approaches can be complementary, and in combination, facilitate a definitive detection and precise characterisation of Kepler-37d. Its RV semi-amplitude of 1.22+/-0.31m/s (mass 5.4+/-1.4M_{Earth}_) is formally consistent with TOI-178b's 1.05^+0.25^_-0.30_m/s, the latter being the smallest detected RV signal of any transiting planet to date, though dynamical simulations suggest Kepler-37d's mass may be on the lower end of our 1{sigma} credible interval. Its consequent density is consistent with either a water-world or that of a gaseous envelope (~0.4% by mass) surrounding a rocky core. Based on RV modelling and a re-analysis of Kepler-37 TTVs, we also argue that the putative (non-transiting) planet Kepler-37e should probably be stripped of its 'confirmed' status.
- ID:
- ivo://CDS.VizieR/J/A+A/594/A54
- Title:
- A 1689 HAWK-I J-band image
- Short Name:
- J/A+A/594/A54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a ground-based, near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z=0.18, which is one of the most powerful gravitational telescopes that nature provides. Our survey was based on multi-epoch J-band observations with the HAWK-I instrument on VLT, with supporting optical data from the Nordic Optical Telescope. Our search resulted in the discovery of five photometrically classified, core-collapse supernovae with high redshifts of 0.671<z<1.703 and magnifications in the range {DELTA}m=-0.31 to -1.58mag, as calculated from lensing models in the literature. Owing to the power of the lensing cluster, the survey had the sensitivity to detect supernovae up to very high redshifts, z~3, albeit for a limited region of space. We present a study of the core-collapse supernova rates for 0.4<=z<2.9, and find good agreement with previous estimates and predictions from star formation history. During our survey, we also discovered two Type Ia supernovae in A 1689 cluster members, which allowed us to determine the cluster Ia rate to be 0.14+0.19-0.09+/-0.01SNuB*h^2^ (SNuB=10^-12^SNeL_{sun},B_^-1^yr^-1^), where the error bars indicate 1{sigma} confidence intervals, statistical and systematic, respectively. The cluster rate normalized by the stellar mass is 0.10+0.13-0.096+/-0.02 in SNuM*h^2^ (SNuM=10^-12^SNeM_{sun}_^-1^yr^-1^). Furthermore, we explore the optimal future survey for improving the core-collapse supernova rate measurements at z>~2 using gravitational telescopes, and for detections with multiply lensed images, and we find that the planned WFIRST space mission has excellent prospects.
706. AH Cam
- ID:
- ivo://CDS.VizieR/J/AJ/107/679
- Title:
- AH Cam
- Short Name:
- J/AJ/107/679
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Analysis of 746 new V-band observations of the RR Lyrae star AH Cam obtained during 1989-1992 clearly show that its light curve cannot be described by a single period. In fact, at first glance, the Fourier spectrum of the photometry resembles that of a double-mode pulsator, with peaks at a fundamental period of 0.3686d and an apparent secondary period of 0.2628d. Nevertheless, the dual-mode solution is a poor fit to the data. Rather, we believe that AH Cam is a single-mode RR Lyrae star undergoing the Blazhko effect: periodic modulation of the amplitude and shape of its light curve. What was originally taken to be the period of the second mode is instead the 1-cycle/d alias of a modulation sidelobe in the Fourier spectrum. The data are well described by a modulation period of just under 11d, which is the shortest Blazhko period reported to date in the literature and confirms the earlier suggestion by Goranskii. A low-resolution spectrum of AH Cam indicates that it is relatively metal rich, with {DELTA}S<=2. Its high metallicity and short modulation period may provide a critical test of at least one theory for the Blazhko effect. Moskalik's internal resonance model makes specific predictions of the growth rate of the fundamental mode vs fundamental period. AH Cam falls outside the regime of other known Blazhko variables and resonance model predictions, but these are appropriate for metal-poor RR Lyrae stars. If the theory matches the behavior of AH Cam for a metal-rich stellar model, this would bolster the resonance hypothesis.
- ID:
- ivo://CDS.VizieR/J/A+A/367/111
- Title:
- A Hipparcos study of the Hyades cluster
- Short Name:
- J/A+A/367/111
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hipparcos trigonometric parallaxes fix distances to individual stars in the Hyades cluster with an accuracy of about 6 percent. We use the Hipparcos and Tycho-2 proper motions, which have a larger relative precision than the Hipparcos trigonometric parallaxes, to derive 3 times more precise distance estimates, by assuming that all members share the same space motion. These so-called secular parallaxes are, as a set, statistically consistent with the Hipparcos parallaxes (Section 6). Table A1 contains, for all 218 members identified by Perryman et al. (1998A&A...331...81P; see also Cat. <J/A+A/331/81>; see Sections 4.1 and 5.1), the trigonometric parallaxes, the Hipparcos and Tycho-2 secular parallaxes, their errors and goodness-of-fit parameters (Sections 2.2 and 5.4), as well as fundamental stellar parameters (Section 9) based on the Hipparcos secular parallaxes and the V-band magnitudes (field H5) and B-V colours (field H37) listed in the Hipparcos Catalogue (1997HIP...C......0E; Cat. <I/239>). Table A2 lists 15 new Hyades candidates (see Sections 4.2 and 5.2) selected by the membership methods developed by de Bruijne (1999MNRAS.306..381D) and Hoogerwerf et al. (1999MNRAS.306..394H) which use proper motion and trigonometric parallax data. Based on photometric, radial velocity, and secular parallax data, we conclude that only one of these stars (HIP 19757) is a likely new member (see Sections 4.2 and 5.2 for details).
- ID:
- ivo://CDS.VizieR/J/A+AS/112/347
- Title:
- A Homogeneous Bright QSO Survey
- Short Name:
- J/A+AS/112/347
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the first paper in a series aimed at defining a statistically significant sample of QSOs in the range 15<B<18.75 and 0.3<z<2.2. The selection is carried out using direct plates obtained at the ESO and UK Schmidt Telescopes, scanned with the COSMOS facility and searched for objects with an ultraviolet excess. Follow-up spectroscopy, carried out at ESO La Silla, is used to classify each candidate. In this initial paper, we describe the scientific objectives of the survey; the selection and observing techniques used. We present the first sample of 285 QSOs (M_B_<-23) in a 153 sq.deg area, covered by the six "deep" fields, intended to obtain significant statistics down B=~18.75 with unprecedented photometric accuracy. From this database, QSO counts are determined in the magnitude range 17<B<18.75.
- ID:
- ivo://CDS.VizieR/J/ApJ/815/33
- Title:
- A Hubble diagram for quasars
- Short Name:
- J/ApJ/815/33
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new method to test the {Lambda}CDM cosmological model and to estimate cosmological parameters based on the nonlinear relation between the ultraviolet and X-ray luminosities of quasars. We built a data set of 1138 quasars by merging several samples from the literature with X-ray measurements at 2keV and SDSS photometry, which was used to estimate the extinction-corrected 2500{AA} flux. We obtained three main results: (1) we checked the nonlinear relation between X-ray and UV luminosities in small redshift bins up to z~6, confirming that the relation holds at all redshifts with the same slope; (2) we built a Hubble diagram for quasars up to z~6, which is well matched to that of supernovae in the common z=0-1.4 redshift interval and extends the test of the cosmological model up to z~6; and (3) we showed that this nonlinear relation is a powerful tool for estimating cosmological parameters. Using the present data and assuming a {Lambda}CDM model, we obtain {Omega}_M_=0.22_-0.08_^+0.10^ and {Omega}_{Lambda}_=0.92-0.30_^+0.18^ ({Omega}=0.28+/-0.04 and {Omega}_{Lambda}_=0.73+/-0.08 from a joint quasar-SNe fit). Much more precise measurements will be achieved with future surveys. A few thousand SDSS quasars already have serendipitous X-ray observations from Chandra or XMM-Newton, and at least 100000 quasars with UV and X-ray data will be made available by the extended ROentgen Survey with an Imaging Telescope Array all-sky survey in a few years. The Euclid, Large Synoptic Survey Telescope, and Advanced Telescope for High ENergy Astrophysics surveys will further increase the sample size to at least several hundred thousand. Our simulations show that these samples will provide tight constraints on the cosmological parameters and will allow us to test for possible deviations from the standard model with higher precision than is possible today.
- ID:
- ivo://CDS.VizieR/J/PAZh/43/460
- Title:
- AI CMi UBV light curves
- Short Name:
- J/PAZh/43/460
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The U BV photometry and low-resolution spectroscopy for the semiregular variable AI CMi, a candidate for post-AGB objects, performed in 1996-2016 and 2000-2013, respectively, are presented. The star showed multiperiodic brightness variations with an amplitude up to 1.5m in the V band, a significant (up to 0.4m) bluing of the B-V and U-B colors as the star faded, and a change of its spectrum from G5 I to K3-5 I, depending on its brightness. A possible long-term fading of AI CMi below 8.5m in the period from May 2013 to early 2015 is observed in the light curve. The colors in this episode did not change the pattern of their unusual behavior with brightness. The main feature of the spectrum for AI CMi is the appearance and strengthening of TiO absorption bands as its brightness declines, which are atypical in the spectra of ordinary G5-K3 supergiants. The bluing of the B-V and U-B colors is interpreted as the blanketing of stellar radiation predominantly in V (and to a lesser extent in B) by the TiO absorption bands whose intensity increases dramatically with decreasing brightness. Another cause of the bluing can be the scattering of stellar radiation by small dust particles in the gas-dust shell of AI CMi. The star's continuum-normalized spectra over the period from 2000 to 2013 in the wavelength range 4200 to 7700 or 9200{AA} are presented. These were taken at different phases of the pulsation cycle and clearly demonstrate the behavior of the TiO absorption bands depending on the V magnitude and B-V color. The equivalent widths of individual TiO bands were measured, and their correlation with the photometric parameters of the star is shown. AI CMi belongs to the O-rich branch of AGB/post-AGB supergiants and has a luminosity of ~4000L_{sun}_ at a distance of 1500+/-700pc. The mass of AI CMi is most likely small and close to the lower mass limit for post-AGB stars. The connection of the star's pulsational activity and nonstationary wind with the formation of its molecular and dust shells is discussed briefly.
