- ID:
- ivo://CDS.VizieR/J/A+A/645/A30
- Title:
- SB updated census in SACY sample
- Short Name:
- J/A+A/645/A30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Nearby young associations offer one of the best opportunities for a detailed study of the properties of young stellar and substellar objects thanks to their proximity (<200pc) and age (~5-150Myr). Previous works have identified spectroscopic (<5au) binaries, close (5-1000au) visual binaries, and wide or extremely wide (1000-100000au) binaries in the young associations. Inmost of the previous analyses, single-lined spectroscopic binaries (SB1) were identified based on radial velocities variations. However, this apparent variation may also be caused by mechanisms unrelated to multiplicity. We seek to update the spectroscopy binary fraction of the Search for Associations Containing Young stars (SACY) sample, taking into consideration all possible biases in our identification of binary candidates, such as activity and rotation. Using high-resolution spectroscopic observations, we produced ~1300 cross-correlation functions (CCFs) to disentangle the previously mentioned sources of contamination. The radial velocity values we obtained were cross-matched with the literature and then used to revise and update the spectroscopic binary (SB) fraction in each object of the SACY association. In order to better describe the CCF profile, we calculated a set of high-order cross-correlation features to determine the origin of the variations in radial velocities. We identified 68 SB candidates from our sample of 410 objects. Our results hint that at the possibility that the youngest associations have a higher SB fraction. Specifically, we found sensitivity-corrected SB fractions of 22^+15^_-11_% for {epsilon} Cha, 31^+16^_-14_% for TW Hya and 32^+9^_-8_% for {beta} Pictoris, in contrast to the five oldest associations we have sampled (~35-125Myr) which are ~10% or lower. This result seems independent of the methodology used to asses membership to the associations. The new CCF analysis, radial velocity estimates, and SB candidates are particularly relevant for membership revision of targets in young stellar associations. These targets would be ideal candidates for follow-up campaigns using high-resolution techniques to confirm binarity, resolve orbits, and, ideally, calculate dynamical masses. Additionally, if the results on the SB fraction in the youngest associations were confirmed, it could hint at a non-universal multiplicity among SACY associations.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/671/1800
- Title:
- SCUBA observations of {rho} Oph cloud
- Short Name:
- J/ApJ/671/1800
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new multiwavelength submillimeter continuum measurements of the circumstellar dust around 48 young stars in the rho Ophiuchi dark clouds. Supplemented with previous 1.3mm observations of an additional 99 objects from the literature, the statistical distributions of disk masses and submillimeter colors are calculated and compared to those in the Taurus-Auriga region. These basic submillimeter properties of young stellar objects in both environments are shown to be essentially identical.
- ID:
- ivo://CDS.VizieR/J/A+A/551/A34
- Title:
- SED information for CrA members
- Short Name:
- J/A+A/551/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The CrA region and the Coronet cluster form a nearby (138pc), young (1-2Myr) star-forming region that hosts a moderate population of Class I, II, and III objects. We study the structure of the cluster and the properties of the protostars and protoplanetary disks in the region. We present Herschel PACS photometry at 100 and 160um, obtained as part of the Herschel Gould Belt Survey. The Herschel maps reveal the cluster members within the cloud with high sensitivity and high dynamic range.
- ID:
- ivo://CDS.VizieR/J/AJ/147/140
- Title:
- SED of 24 class I and class II FU Orionis stars
- Short Name:
- J/AJ/147/140
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- FU Orionis stars (FUors) are eruptive pre-main sequence objects thought to represent quasi-periodic or recurring stages of enhanced accretion during the low-mass star-forming process. We characterize the sample of known and candidate FUors in a homogeneous and consistent way, deriving stellar and circumstellar parameters for each object. We emphasize the analysis in those parameters that are supposed to vary during the FUor stage. We modeled the spectral energy distributions of 24 of the 26 currently known FUors, using the radiative transfer code of Whitney et al. We compare our models with those obtained by Robitaille et al. for Taurus class II and I sources in quiescence periods by calculating the cumulative distribution of the different parameters. FUors have more massive disks: we find that ~80% of the disks in FUors are more massive than any Taurus class II and I sources in the sample. Median values for the disk mass accretion rates are ~10^-7^M_{sun}_/yr versus ~10^-5^M_{sun}_/yr for standard young stellar objects (YSOs) and FUors, respectively. While the distributions of envelope mass accretion rates for class I FUors and standard class I objects are similar, FUors, on average, have higher envelope mass accretion rates than standard class II and class I sources. Most FUors (~70%) have envelope mass accretion rates above 10^-7^M_{sun}_/yr. In contrast, 60% of the classical YSO sample has an accretion rate below this value. Our results support the current scenario in which changes experimented by the circumstellar disk explain the observed properties of these stars. However, the increase in the disk mass accretion rate is smaller than theoretically predicted, although in good agreement with previous determinations.
- ID:
- ivo://CDS.VizieR/J/A+A/651/A70
- Title:
- SHINE sample definition
- Short Name:
- J/A+A/651/A70
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/158/68
- Title:
- 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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/356/89
- Title:
- sigma Ori low-mass stars
- Short Name:
- J/MNRAS/356/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/508/1509
- Title:
- Sky maps for hot Jupiters
- Short Name:
- J/A+A/508/1509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The findings of more than 350 extrasolar planets, most of them nontransiting Hot Jupiters, have revealed correlations between the metallicity of the main-sequence (MS) host stars and planetary incidence. This connection can be used to calculate the planet formation probability around other stars, not yet known to have planetary companions. Numerous wide-field surveys have recently been initiated, aiming at the transit detection of extrasolar planets in front of their host stars. Depending on instrumental properties and the planetary distribution probability, the promising transit locations on the celestial plane will differ among these surveys. We want to locate the promising spots for transit surveys on the celestial plane and strive for absolute values of the expected number of transits in general. Our study will also clarify the impact of instrumental properties such as pixel size, field of view (FOV), and magnitude range on the detection probability. We used data of the Tycho catalog for ~1 million objects to locate all the stars with 0^m^~<m_V_~<11.5^m^ on the celestial plane. We took several empirical relations between the parameters listed in the Tycho catalog, such as distance to Earth, m_V_, and (B-V), and those parameters needed to account for the probability of a star to host an observable, transiting exoplanet. The empirical relations between stellar metallicity and planet occurrence combined with geometrical considerations were used to yield transit probabilities for the MS stars in the Tycho catalog. Magnitude variations in the FOV were simulated to test whether this fluctuations would be detected by BEST, XO, SuperWASP and HATNet.
- ID:
- ivo://CDS.VizieR/J/A+A/393/887
- Title:
- SMC Be stars candidates
- Short Name:
- J/A+A/393/887
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recently the OGLE experiment has provided accurate light curves and colours for about 2 millions stars in the Small Magellanic Cloud. We have examined this database for its content of Be stars, applying some selection criteria, and we have found a sample of ~1000 candidates. Some of these stars show beautiful light curves with amazing variations never observed in any Galactic variable. We find outbursts in 13% of the sample (type-1 stars), high and low states in 15%, periodic variations in 7%, and the usual variations seen in Galactic Be stars in 65% of the cases. The Galactic counterparts of type-1 objects could be the outbursting Be stars found by Hubert & Floquet (1998, Cat. J/A+A/335/565) after the analysis of Hipparcos photometry. We discuss the possibility that type-1 stars could correspond to Be stars with accreting white dwarf companions or alternatively, blue pre-main sequence stars surrounded by thermally unstable accretion disks. We provide coordinates and basic photometric information for these stars and some examples of light curves.
- ID:
- ivo://CDS.VizieR/J/A+A/655/A51
- Title:
- Solar evolutionary and structure models
- Short Name:
- J/A+A/655/A51
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- In protoplanetary disks, the growth and inward drift of dust lead to the generation of a temporal "pebble wave" of increased metallicity. This phase must be followed by a phase in which the exhaustion of the pebbles in the disk and the formation of planets lead to the accretion of metal-poor gas. At the same time, disk winds may lead to the selective removal of hydrogen and helium from the disk. Hence, stars grow by accreting gas that has an evolving composition. In this work, we investigated how the formation of the Solar System may have affected the composition and structure of the Sun, and whether it plays any role in solving the so-called solar-abundance problem, that is, the fact that standard models with up-to-date lower-metallicity abundances reproduce helioseismic constraints significantly more poorly than those with old higher-metallicity abundances. We simulated the evolution of the Sun from the protostellar phase to the present age and attempted to reproduce spectroscopic and helioseismic constraints. We performed chi-squared tests to optimize our input parameters, which we extended by adding secondary parameters. These additional parameters accounted for the variations in the composition of the accreted material and an increase in the opacities. We confirmed that, for realistic models, planet formation occurs when the solar convective zone is still massive; thus, the overall changes due to planet formation are too small to significantly improve the chi-square fits. We found that solar models with up-to-date abundances require an opacity increase of 12% to 18% centered at T=10^6.4^K to reproduce the available observational constraints. This is slightly higher than, but is qualitatively in good agreement with, recent measurements of higher Fe opacities. These models result in better fits to the observations than those using old abundances; therefore, they are a promising solution to the solar abundance problem. Using these improved models, we found that planet formation processes leave a small imprint in the solar core, whose metallicity is enhanced by up to 5%. This result can be tested by accurately measuring the solar neutrino flux. In the improved models, the protosolar molecular cloud core is characterized by a primordial metallicity in the range Zproto=0.0127-0.0157 and a helium mass fraction in the range Yproto=0.268-0.274.
