- ID:
- ivo://CDS.VizieR/J/MNRAS/434/806
- Title:
- Pre-main-sequence isochrones. II. SFR
- Short Name:
- J/MNRAS/434/806
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived ages for 13 young (<30Myr) star-forming regions and find that they are up to a factor of 2 older than the ages typically adopted in the literature. This result has wide-ranging implications, including that circumstellar discs survive longer (=~10-12Myr) and that the average Class I lifetime is greater (=~1Myr) than currently believed. For each star-forming region, we derived two ages from colour-magnitude diagrams. First, we fitted models of the evolution between the zero-age main sequence and terminal-age main sequence to derive a homogeneous set of main-sequence ages, distances and reddenings with statistically meaningful uncertainties. Our second age for each star-forming region was derived by fitting pre-main-sequence stars to new semi-empirical model isochrones. For the first time (for a set of clusters younger than 50Myr), we find broad agreement between these two ages, and since these are derived from two distinct mass regimes that rely on different aspects of stellar physics, it gives us confidence in the new age scale. This agreement is largely due to our adoption of empirical colour-T_eff_ relations and bolometric corrections for pre-main-sequence stars cooler than 4000K. The revised ages for the star-forming regions in our sample are: ~2Myr for NGC 6611 (Eagle Nebula; M 16), IC 5146 (Cocoon Nebula), NGC 6530 (Lagoon Nebula; M 8) and NGC 2244 (Rosette Nebula); ~6Myr for {sigma} Ori, Cep OB3b and IC 348; ~10Myr for {lambda} Ori (Collinder 69); ~11Myr for NGC 2169; ~12Myr for NGC 2362; ~13Myr for NGC 7160; ~14Myr for {chi}Per (NGC 884); and ~20Myr for NGC 1960 (M 36).
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/658/480
- Title:
- Pre-main-sequence stars in Lupus association
- Short Name:
- J/ApJ/658/480
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kinematical analysis of spectroscopically identified pre-main-sequence stars associated with the Lupus dark cloud reveals a streamlike motion of low internal velocity dispersion (<=1.3km/s). A statistically significant mismatch between the convergent point radial velocity and the spectroscopic radial velocity from the literature indicates a moderate degree of expansion. The rate of expansion is too low to account for the present extent of the association if one assumes that the spatially dispersed population was formed in the dense molecular cores observed today. Therefore, it is unlikely that the outlying weak-lined T Tauri members were born in the same star-forming cores as the more compactly located classical T Tauri stars, despite the kinematic integrity of the association. Distances inferred from the classical moving-cluster method show a large depth of the association (~80pc) along the line of sight. A color-magnitude diagram of the association in the near-IR colors corrected for the distribution of distances shows a clear gap separating the older (5-27Myr) and the younger (~1Myr) generations of stars. Half of the identified 1Myr old stars lie in the tight group of mostly classical T Tauri stars associated with the Lupus 3 dark filament. This nest of very young stars appears to be 25pc farther from the Sun than the center of the greater Lupus association.
- ID:
- ivo://CDS.VizieR/J/AJ/154/46
- Title:
- Proper motions and photometry for members of Cha I
- Short Name:
- J/AJ/154/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a search for planetary-mass brown dwarfs in the Chamaeleon I star-forming region using proper motions and photometry measured from optical and infrared images from the Spitzer Space Telescope, the Hubble Space Telescope, and ground-based facilities. Through near-IR spectroscopy at Gemini Observatory, we have confirmed six of the candidates as new late-type members of Chamaeleon I ({>=}M8). One of these objects, ChaJ11110675-7636030, has the faintest extinction-corrected M_K_ among known members, which corresponds to a mass of 3-6M_Jup_ according to evolutionary models. That object and two other new members have redder mid-IR colors than young photospheres at {<=}M9.5, which may indicate the presence of disks. However, since those objects may be later than M9.5 and the mid-IR colors of young photospheres are ill-defined at those types, we cannot determine conclusively whether color excesses from disks are present. If ChaJ11110675-7636030 does have a disk, it would be a contender for the least-massive known brown dwarf with a disk. Since the new brown dwarfs that we have found extend below our completeness limit of 6-10M_Jup_, deeper observations are needed to measure the minimum mass of the initial mass function in Chamaeleon I.
- ID:
- ivo://CDS.VizieR/V/27
- Title:
- Proper Motions and UBV Photometry in h+{chi} Per
- Short Name:
- V/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Proper motions with an 80 year baseline have been determined relative to reference stars with B=13.9mag. determined for 3086 stars brighter than B=15.5mag. within an area of 50' radius, centered at RA=2h16.9m, Dec=+57{deg}01' (1950.0). Two pairs of Tashkent normal astrograph plates with a mean epoch difference of 80 years was used. Proper motions were also measured for 1055 stars with 15.5 <= B <= 17.1 mag. in two areas 14' in radius, centered on the h and {chi} Persei clusters. Proper motions are also given for 1386 stars in an adjacent area (RA=2h06.7m, Dec=+56{deg}57') for 1386 stars with a 38 year baseline. The mean errors of the proper motions are equal in right ascension and declination. For the h and {chi} Perseus region, they are 0.0021"/yr and for the adjacent region, they are 0.0031"/yr. The proper motions in the adjacent area have been reduced to the system of those in the cluster region using 214 stars in common. UBV magnitudes of the stars were determined using plates taken with the 80/120/240 Schmidt telescope of the Radioastrophysical Observatory of the Academy of Sciences of the Latvian SSR and photoelectric standards published by Johnson and Morgan (1955ApJ...122..429J) and Widley (1964ApJS....8..439W). The number of measured plates and the corresponding errors are given in the following table: ----------------------------------------------------- FILE NAME # PLATES ERRORS (0.01mag) V B U V B U ----------------------------------------------------- data1.dat 2 3 2 6 5 6 data2.dat 1 2 - 8 6 - adjarea.dat 2 2 2 6 6 6 _____________________________________________________ Cluster members were selected on the basis of their proper motion and photometric criteria. The membership probability was calculated on the assumption of a normal distribution of the proper motions around the cluster proper motion.
- ID:
- ivo://CDS.VizieR/J/A+A/504/981
- Title:
- Proper motions of cool stars in Upper Sco OB
- Short Name:
- J/A+A/504/981
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Proper motion measurements of the cool and ultracool populations in the Upper Scorpius OB association are crucial to confirm membership and to identify possible run-away objects. We cross-match samples of photometrically selected and spectroscopically confirmed cool and ultracool (K5<SpT<M8.5) candidate members in the Upper Scorpius OB association using the literature and the USNO-B (Cat. <I/284>) and the UCAC2 (Cat. <I/294>) catalogues. 251 of these objects have a USNO-B and/or UCAC2 counterpart with proper motion measurements.
- ID:
- ivo://CDS.VizieR/J/A+A/361/1143
- Title:
- Proper motions of PMS stars
- Short Name:
- J/A+A/361/1143
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present proper motion measurements of pre-main sequence (PMS) stars associated with major star-forming regions of the southern hemisphere (Chamaeleon, Lupus, Upper Scorpius - Ophiuchus, Corona Australis), situated in the galactic longitude range l=290{deg} to l=360{deg}. A list of PMS stars as complete as possible was established based on the Herbig and Bell (1988LicOB1111....1H) catalogue and many new catalogues like the PDS survey, the catalogue of Herbig Ae/Be stars by The et al. (1994A&AS..104..315T), X-rays surveys, etc. The measurements made use of public material (mainly AC2000 and USNO-A2.0 catalogues) as well as scans of SERC-J Schmidt plates with the MAMA measuring machine (Paris) and Valinhos CCD meridian circle observations (Brazil). We derived proper motions for 213 stars, with an accuracy of 5 to 10mas/yr depending mainly on the difference of epochs between the position sources. The main characteristics of the sample are discussed. We show that systematic motions of groups of stars exist, which are not explained by the reflex solar motion.
- ID:
- ivo://CDS.VizieR/J/A+A/523/A23
- Title:
- Properties of OB associations in IC 1613
- Short Name:
- J/A+A/523/A23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To understand the structure and evolution of massive stars, systematic surveys of the Local Group galaxies have been undertaken, to find these objects in environments of different chemical abundances. We focus on the metal-poor irregular galaxy IC 1613 to analyze the stellar and wind structure of its low-metallicity massive stars. We ultimately aim to study the metallicity-dependent driving mechanism of the winds of blue massive stars and use metal-poor massive stars of the Local Volume as a proxy for the stars in the early Universe. In a previous paper we produced a list of OB associations in IC 1613. Their properties are not only a powerful aid towards finding the most interesting candidate massive stars, but also reveal the structure and recent star formation history of the galaxy. We characterize these OB associations and study their connection with the galactic global properties. The reddening-free Q parameter is a powerful tool in the photometric analysis of young populations of massive stars, since it exhibits a smaller degree of degeneracy with OB spectral types than the B-V color. The color-magnitude diagram (Q vs. V) of the OB associations in IC 1613 is studied to determine their age and mass, and confirm the population of young massive stars. We identified more than 10 stars with M>=50M_{sun}_. Spectral classification available for some of them confirm their massive nature, yet we find the common discrepancy with the spectroscopically derived masses. There is a general increasing trend of the mass of the most massive member with the number of members of each association, but not with the stellar density. The average diameter of the associations of this catalog is 40pc, half the historically considered typical size of OB associations. Size increases with the association population. The distribution of the groups strongly correlates with that of neutral and ionized hydrogen. We find the largest dispersion of association ages in the bubble region of the galaxy where hydrogen is abundant, implying that recent star formation has proceeded over a longer period of time than in the rest of the galaxy, and is still ongoing. Very young associations are found at the west of the galaxy far from the bubble region, traditionally considered the sole locus of star formation, but still rich in neutral hydrogen. The contrast in the stellar properties derived from photometry and spectroscopy (when the latter is available) shows that the Q pseudo-color is very useful for estimating the parameters of OB stars when only photometric observations exist. This work helped define an extensive pool of candidate OB stars for subsequent spectroscopic analyses designed to study the structure and winds of metal-poor massive stars.
- ID:
- ivo://CDS.VizieR/J/AJ/154/129
- Title:
- PSYM-WIDE: planetary-mass companions to YMG members
- Short Name:
- J/AJ/154/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a direct imaging survey for very large separation (>100 AU), low-mass companions around 95 nearby young K5-L5 stars and brown dwarfs. They are high-likelihood candidates or confirmed members of the young (~<150 Myr) {beta} Pictoris and AB Doradus moving groups (ABDMG) and the TW Hya, Tucana-Horologium, Columba, Carina, and Argus associations. Images in i' and z' filters were obtained with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South to search for companions down to an apparent magnitude of z'~22-24 at separations >~20" from the targets and in the remainder of the wide 5.5'x5.5' GMOS field of view. This allowed us to probe the most distant region where planetary-mass companions could be gravitationally bound to the targets. This region was left largely unstudied by past high-contrast imaging surveys, which probed much closer-in separations. This survey led to the discovery of a planetary-mass (9-13 M_Jup_) companion at 2000 AU from the M3V star GU Psc, a highly probable member of ABDMG. No other substellar companions were identified. These results allowed us to constrain the frequency of distant planetary-mass companions (5-13 M_Jup_) to 0.84_-0.66_^+6.73^% (95% confidence) at semimajor axes between 500 and 5000 AU around young K5-L5 stars and brown dwarfs. This is consistent with other studies suggesting that gravitationally bound planetary-mass companions at wide separations from low-mass stars are relatively rare.
- ID:
- ivo://CDS.VizieR/J/A+AS/77/447
- Title:
- Puppis window UBV photometry
- Short Name:
- J/A+AS/77/447
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photographic UBV photometry of 1302 stars in a 76 square-arcminute field in the Puppis window to U~16.9, (B, V)~21 is presented. The presence of an OB association at r~6kpc in this direction as reported by Stetson and FitzGerald (1985) is confirmed. No evidence of any more distant early-type stars is indicated.
- ID:
- ivo://CDS.VizieR/J/ApJ/751/4
- Title:
- Radial velocities of massive stars in Cyg OB2
- Short Name:
- J/ApJ/751/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This work provides a statistical analysis of the massive star binary characteristics in the Cygnus OB2 association using radial velocity information of 114 B3-O5 primary stars and orbital properties for the 24 known binaries. We compare these data to a series of Monte Carlo simulations to infer the intrinsic binary fraction and distributions of mass ratios, periods, and eccentricities. We model the distribution of mass ratio, log-period, and eccentricity as power laws and find best-fitting indices of {alpha}=0.1+/-0.5, {beta}=0.2+/-0.4, and {gamma}=-0.6+/-0.3, respectively. These distributions indicate a preference for massive companions, short periods, and low eccentricities. Our analysis indicates that the binary fraction of the cluster is 44%+/-8% if all binary systems are (artificially) assumed to have P<1000 days; if the power-law period distribution is extrapolated to 10^4^ years, then a plausible upper limit for bound systems, the binary fraction is ~90%+/-10%. Of these binary (or higher order) systems, ~45% will have companions close enough to interact during pre- or post-main-sequence evolution (semi-major axis <~4.7AU). The period distribution for P<26 days is not well reproduced by any single power law owing to an excess of systems with periods around 3-5 days (0.08-0.31AU) and a relative shortage of systems with periods around 7-14 days (0.14-0.62AU). We explore the idea that these longer-period systems evolved to produce the observed excess of short-period systems. The best-fitting binary parameters imply that secondaries generate, on average, ~16% of the V-band light in young massive populations. This means that photometrically based distance measurements for young massive clusters and associations will be systematically low by ~8% (0.16 mag in the distance modulus) if the luminous contributions of unresolved secondaries are not taken into account.
