- ID:
- ivo://CDS.VizieR/J/ApJ/875/64
- Title:
- Polarization & photom. of stars toward LDN1225
- Short Name:
- J/ApJ/875/64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results based on the optical R-band observations of the polarization of 280 stars distributed toward the dark globule LDN1225. Parallaxes from Gaia data release 2 along with the polarization data of ~200 stars have been used to (a) constrain the distance of LDN 1225 as 830+/-83pc, (b) determine the contribution of interstellar polarization, and (c) characterize the dust properties and delineate the magnetic field (B-field) morphology of LDN 1225. We find that B-fields are more organized and exhibit a small dispersion of 12{deg}. Using the ^12^CO molecular line data from the Purple Mountain Observatory, along with the column density and dispersion in B-fields, we estimate the B-field strength to be ~56+/-10{mu}G, the ratio of magnetic to turbulent pressure to be ~3+/-2, and the ratio of mass to magnetic flux (in units of the critical value) to be <1. These results indicate the dominant role of B-fields in comparison to turbulence and gravity in rendering the cloud support. B-fields are aligned parallel to the low-density parts (traced by a ^12^CO map) of the cloud; in contrast, they are neither parallel nor perpendicular to the high-density core structures (traced by ^13^CO and C^18^O maps). LDN1225 hosts two 70{mu}m sources, which seem to be low-mass Class 0 sources. The ratio of total to selective extinction derived using optical and near-infrared photometric data is found to be anomalous (RV=3.4), suggesting the growth of dust grains in LDN 1225. The polarization efficiency of dust grains follows a power law with an index of -0.7, implying that optical polarimetry traces B-fields in the outer parts of the cloud.
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- ID:
- ivo://CDS.VizieR/J/ApJ/794/31
- Title:
- Post-merger cluster A2255 membership
- Short Name:
- J/ApJ/794/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The effects of dense environments on normal field galaxies are still up for debate despite much study since Abell published his catalog of nearby clusters in 1958 (1958ApJS....3..211A). There are changes in color, morphology, and star formation properties when galaxies fall into groups and clusters, but the specifics of how and where these modifications occur are not fully understood. To look for answers, we focused on star-forming galaxies in A2255, an unrelaxed cluster thought to have recently experienced a merger with another cluster or large group. We used H{alpha}, MIPS 24 {mu}m, and WISE 22 {mu}m to estimate total star formation rates (SFRs) and Sloan Digital Sky Survey photometry to find stellar masses (M_*_) for galaxies out to ~5 r_200_. We compared the star-forming cluster galaxies with the field SFR-mass distribution and found no enhancement or suppression of star formation in currently star-forming galaxies of high mass (log(M_*_/M_{sun}_)>~10). This conclusion holds out to very large distances from the cluster center. However, the core (r_proj_<3 Mpc) has a much lower fraction of star-forming galaxies than anywhere else in the cluster. These results indicate that for the mass range studied here, the majority of the star formation suppression occurs in the core on relatively short timescales, without any enhancement prior to entering the central region. If any significant enhancement or quenching of star formation occurs, it will be in galaxies of lower mass (log(M_*_/M_{sun}_)<10).
- ID:
- ivo://CDS.VizieR/J/AJ/124/1670
- Title:
- Post-T Tauri Stars in Sco-Cen Association
- Short Name:
- J/AJ/124/1670
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a spectroscopic survey of X-ray and proper-motion-selected samples of late-type stars in the Lower Centaurus-Crux (LCC) and Upper Centaurus-Lupus (UCL) subgroups of the nearest OB association: Scorpius-Centaurus. The primary goals of the survey are to determine the star formation history of the OB subgroups and to assess the frequency of accreting stars in a sample dominated by "post-T Tauri" pre-main-sequence (PMS) stars. We investigate two samples: (1) proper-motion candidates from the ACT Catalog (<I/246>) and Tycho Reference Catalog (TRC, <I/250>) with X-ray counterparts in the ROSAT All-Sky Survey (RASS) Bright Source Catalog and (2) G- and K-type stars in the Hipparcos catalog found to be candidate members by de Zeeuw et al. (1999, Cat. <J/AJ/117/354>). We obtained optical spectra of 130 candidates with the Siding Spring 2.3m dual-beam spectrograph.
- ID:
- ivo://CDS.VizieR/J/ApJ/796/48
- Title:
- Potential exoplanet targets with Palomar/TripleSpec
- Short Name:
- J/ApJ/796/48
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Here we explore the capabilities of NASA's 3.0 m Infrared Telescope Facility (IRTF) and SpeX spectrometer and the 5.08 m Hale telescope with the TripleSpec spectrometer with near-infrared H-, K-, and L-band measurements of HD 209458b's secondary eclipse. Our IRTF/SpeX data are the first absolute L-band spectroscopic emission measurements of any exoplanet other than the hot Jupiter HD 189733b. Previous measurements of HD 189733b's L band indicate bright emission hypothesized to result from non-LTE CH_4_{nu}_3_ fluorescence. We do not detect a similar bright 3.3 {mu}m feature to ~3{sigma}, suggesting that fluorescence does not need to be invoked to explain HD 209458b's L-band measurements. The validity of our observation and reduction techniques, which decrease the flux variance by up to 2.8 orders of magnitude, is reinforced by 1{sigma} agreement with existent Hubble/NICMOS and Spitzer/IRAC1 observations that overlap the H, K, and L bands, suggesting that both IRTF/SpeX and Palomar/TripleSpec can measure an exoplanet's emission with high precision.
- ID:
- ivo://CDS.VizieR/J/ApJ/842/83
- Title:
- Praesepe members rotational periods from K2 LCs
- Short Name:
- J/ApJ/842/83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze K2 light curves for 794 low-mass (1>~M_*_>~0.1M_{sun}_) members of the ~650Myr old open cluster Praesepe and measure rotation periods (P_rot_) for 677 of these stars. We find that half of the rapidly rotating >~0.3M_{sun}_ stars are confirmed or candidate binary systems. The remaining >~0.3M_{sun}_ fast rotators have not been searched for companions, and are therefore not confirmed single stars. We previously found that nearly all rapidly rotating 0.3M_{sun}_ stars in the Hyades are binaries, but we require deeper binary searches in Praesepe to confirm whether binaries in these two co-eval clusters have different P_rot_ distributions. We also compare the observed P_rot_ distribution in Praesepe to that predicted by models of angular-momentum evolution. We do not observe the clear bimodal P_rot_ distribution predicted by Brown (2014ApJ...789..101B) for >0.5M_{sun}_ stars at the age of Praesepe, but 0.25-0.5M_{sun}_ stars do show stronger bimodality. In addition, we find that >60% of early M dwarfs in Praesepe rotate more slowly than predicted at 650Myr by Matt+ (2015ApJ...799L..23M), which suggests an increase in braking efficiency for these stars relative to solar-type stars and fully convective stars. The incompleteness of surveys for binaries in open clusters likely impacts our comparison with these models since the models only attempt to describe the evolution of isolated single stars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/347/101
- Title:
- Precision colour-magnitude diagram of M67
- Short Name:
- J/MNRAS/347/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have calibrated and combined an extensive set of BVI observations of M67 to produce a colour-magnitude diagram of stars measured with high relative precision. We have selected stars that are most likely to be single-star members of the cluster using proper motion, radial velocity, and variability information from the literature, and an examination of the most probable colour-magnitude diagram locations of unresolved stellar blends. We have made detailed comparisons of our photometry of the selected stars with theoretical models, and discuss the most notable discrepancies. Observations of M67 turn-off stars are a severe test of algorithms attempting to describe convective cores in the limit of small extent, and we find strong evidence of a 'hook' just fainter than the turn-off gap. The stars in M67 support assertions that the degree of convective core overshooting decreases to zero for stars with masses in the range 1.0<(M/M_{sun}_)<=1.5, but that the degree of overshoot is smaller than currently used in published isochrones. We also verify that all current theoretical models for the lower main sequence (with the exception of Baraffe et al., 1998, Cat. J/A+A/337/403) are too blue for MV>~6, even when the sequences are shifted to match M67 near the MV of the Sun, probably due to a combination of problems with colour-Teff transformations and realistic surface boundary conditions for models. Finally, we identify a subset of cluster members with unusual photometry (candidate red giant binaries, blue straggler stars, and triple systems) deserving of further study.
- 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/A+A/438/769
- Title:
- Pre-main sequence stars Proper Motion Catalog
- Short Name:
- J/A+A/438/769
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalogue presents astrometric (position and proper motion) and photometric parameters for 1250 PMS stars and 104 PMS star candidates spread over all-sky major star-forming regions. We provide for each star the mean (J2000.0) position and proper motion derived from CCD meridian observations(Bordeaux and Valinhos CCD meridian circle), ESOD1.5m and OHP120cm telescopes, Schmidt SERC-J, POSS I and POSS II plates digitized with the MAMA measuring machine (Paris) and published catalogues as AC2000.2 (<I/275>), USNO-A2.0 (<I/252>), HIPPARCOS (<I/239>), Tycho-2 (<I/259>), UCAC2 (<I/289>), 2MASS (<II/246>) and other astrometric sources. We also provide, when available, CCD meridian V magnitude and the J, H, K magnitudes from 2MASS catalogue. Precision on proper motions vary from 2 to 5mas/yr depending on the used sources of ancient positions and depending also on the embedding and binarity of the source. The V limiting magnitude of our catalogue is about 16.5.
- ID:
- ivo://CDS.VizieR/J/ApJ/696/L84
- Title:
- Primordial circumstellar disks in binary systems
- Short Name:
- J/ApJ/696/L84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We combine the results from several multiplicity surveys of pre-main-sequence stars located in four nearby star-forming regions with Spitzer data from three different Legacy Projects. This allows us to construct a sample of 349 targets, including 125 binaries, which we use to to investigate the effect of companions on the evolution of circumstellar disks. We find that the distribution of projected separations of systems with Spitzer excesses is significantly different (P~2.4e-5, according to the K-S test for binaries with separations less than 400AU) from that of systems lacking evidence for a disk. As expected, systems with projected separations less than 40AU are half as likely to retain at least one disk than are systems with projected separations in the 40-400AU range. These results represent the first statistically significant evidence for a correlation between binary separation and the presence of an inner disk (r~1AU). Several factors (e.g., the incompleteness of the census of close binaries, the use of unresolved disk indicators, and projection effects) have previously masked this correlation in smaller samples. We discuss the implications of our findings for circumstellar disk lifetimes and the formation of planets in multiple systems.
- ID:
- ivo://CDS.VizieR/J/ApJS/209/32
- Title:
- Probable young stars in the MYStIX project
- Short Name:
- J/ApJS/209/32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Massive Young star-forming complex Study in Infrared and X-rays (MYStIX) project requires samples of young stars that are likely members of 20 nearby Galactic massive star-forming regions. Membership is inferred from statistical classification of X-ray sources, from detection of a robust infrared excess that is best explained by circumstellar dust in a disk or infalling envelope and from published spectral types that are unlikely to be found among field stars. We present the MYStIX membership lists here, and describe in detail the statistical classification of X-ray sources via a "Naive Bayes Classifier."
