Large surveys with new-generation high-contrast imaging instruments are needed to derive the frequency and properties of exoplanet populations with separations from 5 to 300au. A careful assessment of the stellar properties is crucial for a proper understanding of when, where, and how frequently planets form, and how they evolve. The sensitivity of detection limits to stellar age makes this a key parameter for direct imaging surveys. We describe the SpHere INfrared survey for Exoplanets (SHINE), the largest direct imaging planet-search campaign initiated at the VLT in 2015 in the context of the SPHERE Guaranteed Time Observations of the SPHERE consortium. In this rst paper we present the selection and the properties of the complete sample of stars surveyed with SHINE, focusing on the targets observed during the rst phase of the survey (from February 2015 to February 2017). This early sample composed of 150 stars is used to perform a preliminary statistical analysis of the SHINE data, deferred to two companion papers presenting the survey performance, main discoveries, and the preliminary statistical constraints set by SHINE. We describe the SpHere INfrared survey for Exoplanets (SHINE), the largest direct imaging planet-search campaign initiated at the VLT in 2015 in the context of the SPHERE Guaranteed Time Observations of the SPHERE consortium. In this rst paper we present the selection and the properties of the complete sample of stars surveyed with SHINE, focusing on the targets observed during the first phase of the survey (from February 2015 to February 2017). This early sample composed of 150 stars is used to perform a preliminary statistical analysis of the SHINE data, deferred to two companion papers presenting the survey performance, main discoveries, and the preliminary statistical constraints set by SHINE. Based on a large database collecting the stellar properties of all young nearby stars in the solar vicinity (including kinematics, membership to moving groups, isochrones, lithium abundance, rotation, and activity), we selected the original sample of 800 stars that were ranked in order of priority according to their sensitivity for planet detection in direct imaging with SPHERE. The properties of the stars that are part of the early statistical sample were revisited, including for instance measurements from the GAIA Data Release 2. Rotation periods were derived for the vast majority of the late-type objects exploiting TESS light curves and dedicated photometric observations. The properties of individual targets and of the sample as a whole are presented.
UBVRI data on 36 short-period (P<5days) Cepheids is given. The observing techniques and reduction procedures are described. A consistent set of finding charts, a set of standard stars for each Cepheid, and improved coordinates are also presented.
Short-period variables in young open cluster Stock 8
Short Name:
J/AJ/158/68
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present time-series photometry in the field of Stock 8 and identified 130 short-period variable stars. Twenty-eight main-sequence and 23 pre-main-sequence variables are found to be part of cluster Stock 8. The main-sequence variables are classified as slow pulsators of the B-type, {beta} Cep, and {delta} Scuti stars. Fourteen main-sequence stars could be new class variables as discussed by Mowlavi et al. (2013, J/A+A/554/A108) and Lata et al. (2011MNRAS.418.1346L; 2012MNRAS.427.1449L; 2014, J/MNRAS/442/273; 2016MNRAS.456.2505L). The age and mass of pre-main-sequence variables are found to be ~<5 Myr and in the mass range of 0.5-2.8 M_{sun}_, respectively. These pre-main-sequence stars could be T-Tauri variables. We have found 5 and 2 of 23 pre-main-sequence variables as classical T-Tauri stars and Herbig Ae/Be stars, respectively, whereas 16 pre-main-sequence stars are classified as weak-line T-Tauri stars.
We report the result of our near-infrared survey of short-period variable stars (P<60d) in a field of view of 20'x30' towards the Galactic Centre (GC). Forty-five variables are discovered and we classify the variables based on their light-curve shapes and other evidence. In addition to 3 classical Cepheids reported previously, we find 16 type II Cepheids, 24 eclipsing binaries, 1 pulsating star with P=0.265d (RR Lyr or {delta} Sct) and 1 Cepheid-like variable whose nature is uncertain. Eclipsing binaries are separated into the foreground objects and those significantly obscured by interstellar extinction. One of the reddened binaries contains an O-type supergiant and its light curve indicates an eccentric orbit. We discuss the nature and distribution of type II Cepheids as well as the distance to the GC based on these Cepheids and other distance indicators. The estimates of R_0_(GC) we obtained based on photometric data agree with previous results obtained with kinematics of objects around the GC. Furthermore, our result gives support to the reddening law obtained by Nishiyama and collaborators, A_Ks_/E(H-Ks)=1.44, because a different reddening law would result in a rather different distance estimate.
We present the goals, strategy and first results of the OmegaWhite survey: a wide-field high-cadence g-band synoptic survey which aims to unveil the Galactic population of short-period variable stars (with periods <80min), including ultracompact binary star systems and stellar pulsators. The ultimate goal of OmegaWhite is to cover 400deg^2^ along the Galactic plane reaching a depth of g=21.5mag (10{sigma}), using OmegaCam on the VLT Survey Telescope (VST). The fields are selected to overlap with surveys such as the Galactic Bulge Survey and the VST Photometric H{alpha} Survey of the Southern Galactic Plane for multiband colour information. Each field is observed using 38 exposures of 39s each, with a median cadence of ~2.7min for a total duration of two hours. Within an initial 26deg^2^, we have extracted the light curves of 1.6 million stars, and have identified 613 variable candidates which satisfy our selection criteria. Furthermore, we present the light curves and statistical properties of 20 sources which have the highest likelihood of being variable stars. One of these candidates exhibits the colours and light-curve properties typically associated with ultracompact AM CVn binaries, although its spectrum exhibits weak Balmer absorption lines and is thus not likely to be such a binary system. We also present follow-up spectroscopy of five other variable candidates, which identifies them as likely low-amplitude {delta} Sct pulsating stars.
We present the results of CCD photometry in the seven-color Vilnius system for 922 stars down to V~17mag in a 1.5 square degree field at the northern edge of the HII region Sh2-205, at the Perseus and Camelopardalis border. Using the intrinsic color indices and photometric reddening-free Q-parameters, two-dimensional spectral types for most stars are determined.
Our goal is to probe the populations of obscured and unobscured AGN investigating their optical-IR and X-ray properties as a function of X-ray flux, luminosity and redshift within a hard X-ray selected sample with wide multiwavelength coverage. We selected a sample of 136 X-ray sources detected at a significance of >=3{sigma} in the 2-10keV band (F_2-10_>~10^-14^erg/cm^2^/s) in a ~1deg^2^ area in the XMM Medium Deep Survey (XMDS, Cat. <J/A+A/439/413>). The XMDS area is covered with optical photometry from the VVDS and CFHTLS surveys and infrared Spitzer data from the SWIRE survey. Based on the X-ray luminosity and X-ray to optical ratio, 132 sources are likely AGN, of which 122 have unambiguous optical - IR identification. The observed optical and IR spectral energy distributions of all identified sources are fitted with AGN/galaxy templates in order to classify them and compute photometric redshifts. X-ray spectral analysis is performed individually for sources with a sufficient number of counts and using a stacking technique for subsamples of sources at different flux levels. Hardness ratios are used to estimate X-ray absorption in individual weak sources.
Intermediate-resolution (R~7000) spectroscopy is presented for 76 photometrically selected very low-mass (0.04<M<0.3M_{sun}_) candidate members of the young cluster around sigma Orionis (sigma Ori). More than two-thirds appear to be genuine cluster members on the basis that they exhibit Li I 6708{AA} absorption, weak Na I 8183/8195{AA} features and a radial velocity consistent with the cluster mean. Photometric selection alone therefore appears to be very effective in identifying cluster members in this mass range. Only six objects appear to be certain non-members; however, a substantial subset of 13 candidates have ambiguous or contradictory indications of membership and lack Li absorption. Together with an observed spread in the equivalent width of the Li absorption feature in the cooler stars of our sample, this indicates that there may be deficiencies in our understanding of the formation of this line in cool, low-gravity objects.
We present a spectroscopic survey of the stellar population of the {sigma} Orionis cluster. We have obtained spectral types for 340 stars. Spectroscopic data for spectral typing come from several spectrographs with similar spectroscopic coverage and resolution. More than half of the stars in our sample are members confirmed by the presence of lithium in absorption, strong H{alpha} in emission or weak gravity-sensitive features. In addition, we have obtained high-resolution (R~34000) spectra in the H{alpha} region for 169 stars in the region. Radial velocities were calculated from this data set. The radial velocity distribution for members of the cluster is in agreement with previous work. Analysis of the profile of the H{alpha} line and infrared observations reveals two binary systems or fast rotators that mimic the H{alpha} width expected in stars with accretion disks. On the other hand, there are stars with optically thick disks and narrow H{alpha} profiles not expected in stars with accretion disks. This contribution constitutes the largest homogeneous spectroscopic data set of the {sigma} Orionis cluster to date.
For decades ever since the early detection in the 1990s of the emission spectral features of crystalline silicates in oxygen-rich evolved stars, there is a long-standing debate on whether the crystallinity of the silicate dust correlates with the stellar mass-loss rate. To investigate the relation between the silicate crystallinities and the mass-loss rates of evolved stars, we carry out a detailed analysis of 28 nearby oxygen-rich stars. We derive the mass-loss rates of these sources by modelling their spectral energy distributions from the optical to the far-infrared. Unlike previous studies in which the silicate crystallinity was often measured in terms of the crystalline-to-amorphous silicate mass ratio, we characterize the silicate crystallinities of these sources with the flux ratios of the emission features of crystalline silicates to that of amorphous silicates. This does not require the knowledge of the silicate dust temperatures, which are the major source of uncertainties in estimating the crystalline-to-amorphous silicate mass ratio. With a Pearson correlation coefficient of ~-0.24, we find that the silicate crystallinities and the mass-loss rates of these sources are not correlated. This supports the earlier findings that the dust shells of low mass-loss rate stars can contain a significant fraction of crystalline silicates without showing the characteristic features in their emission spectra.
