- ID:
- ivo://CDS.VizieR/J/A+A/632/A38
- Title:
- Westerlund 1 reduced images of radio emission
- Short Name:
- J/A+A/632/A38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Massive stars and their stellar winds are important for a number of feedback processes. The mass lost in the stellar wind can help determine the end-point of the star as a neutron star (NS) or a black hole (BH). However, the impact of mass loss on the post-main sequence evolutionary stage of massive stars is not well understood. Westerlund 1 is an ideal astrophysical laboratory in which to study massive stars and their winds in great detail over a large range of different evolutionary phases. We aim to study the radio emission from Westerlund 1, in order to measure radio fluxes from the population of massive stars, and determine the mass-loss rates and spectral indices where possible. Observations were carried out in 2015 and 2016 with the Australia Telescope Compact Array (ATCA) at 5.5 and 9GHz using multiple configurations, with maximum baselines ranging from 750m to 6km. Thirty stars are detected in the radio from the fully concatenated dataset, ten of which are Wolf Rayet stars (WRs) (predominantly late type WN stars), five yellow hypergiants (YHGs), four red supergiants (RSGs), one luminous blue variable (LBV), the sgB[e] star W9, and several OB supergiants. New source detections in the radio are found for the WR stars, and five OB supergiants. These detections lead to evidence for three new OB supergiant binary candidates, which is inferred from derived spectral index limits. Spectral indices and index limits were determined for massive stars in Westerlund 1. For cluster members found to have partially optically thick emission, mass-loss rates were calculated. Under the approximation of a thermally emitting stellar wind and a steady mass-loss rate, clumping ratios were then estimated for eight WRs. Diffuse radio emission was detected throughout the cluster. Detections of knots of radio emission with no known counterparts indicate the highly clumped structure of this intra-cluster medium, likely shaped by a dense cluster wind.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/3797
- Title:
- Westerlund 2 UBVIc photometry
- Short Name:
- J/MNRAS/446/3797
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep UBVI_c_ photometric data of the young open cluster Westerlund 2. An abnormal reddening law of R_V,cl_=4.14+/-0.08 was found for the highly reddened early-type members (E(B-V)>=1.45), whereas a fairly normal reddening law of R_V,fg_=3.33+/-0.03 was confirmed for the foreground early-type stars (E(B-V)_fg_<1.05). The distance modulus was determined from zero-age main-sequence fitting to the reddening-corrected colour-magnitude diagram of the early-type members to be V_0_-M_V_=13.9+/-0.14 (random error) _-0.1_^+0.4^ (the upper limit of systematic error) mag (d=6.0+/-0.4_-0.3_^+1.2^kpc). To obtain te initial mass function, pre-main-sequence (PMS) stars were selected by identifying the optical counterparts of Chandra X-ray sources and mid-infrared emission stars from the Spitzer GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) source catalogue. The initial mass function shows a shallow slope of {Gamma}=-1.1+/-0.1 down to log(m)=0.7. The total mass of Westerlund 2 is estimated to be at least 7400M_{sun}_. The age of Westerlund 2 from the main-sequence turn-on and PMS stars is estimated to be <~1.5Myr. We confirmed the existence of a clump of PMS stars located ~1-arcmin north of the core of Westerlund 2, but we could not find any clear evidence for an age difference between the core and the northern clump.
- ID:
- ivo://CDS.VizieR/J/ApJ/867/62
- Title:
- White dwarf population of Messier 67
- Short Name:
- J/ApJ/867/62
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- White dwarfs (WDs) are excellent forensic tools for studying end-of-life issues surrounding low- and intermediate-mass stars, and the old, solar metallicity open star cluster Messier 67 is a proven laboratory for the study of stellar evolution for solar-type stars. In this paper, we present a detailed spectroscopic study of brighter (M_g_<=12.4) WDs in Messier 67, and in combination with previously published proper motion membership determinations, we identify a clean, representative sample of cluster WDs, including 13 members with hydrogen-dominated atmospheres, at least one of which is a candidate double degenerate, and 5 members with helium-dominated atmospheres. Using this sample we test multiple predictions surrounding the final stages of stellar evolution in solar-type stars. In particular, the stochasticity of the integrated mass lost by ~1.5 solar mass stars is less than 7% of the WD remnant mass. We identify WDs likely resulting from binary evolution, including at least one blue straggler remnant and two helium-core WDs. We observe no evidence of a significant population of helium-core WDs formed by enhanced mass loss on the red giant branch of the cluster. The distribution of WD atmospheric compositions is fully consistent with that in the field, limiting proposed mechanisms for the suppression of helium atmosphere WD formation in star clusters. In short, the WD population of Messier 67 is fully consistent with basic predictions of single- and multiple-star stellar evolution theories for solar metallicity stars.
- ID:
- ivo://CDS.VizieR/J/AJ/132/1669
- Title:
- Wide-field CCD phot. around nine open clusters
- Short Name:
- J/AJ/132/1669
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we study the evolution of the core and corona of nine open clusters using the projected radial density profiles derived from homogeneous CCD photometric data obtained with the 105cm Kiso Schmidt telescope. The age and galactocentric distance of the target clusters vary from 16 to 2000Myr and 9 to 10.8kpc, respectively. Barring Be 62, which is a young open cluster, other clusters show a uniform reddening across the cluster region.
- ID:
- ivo://CDS.VizieR/J/AJ/155/50
- Title:
- WISE photometry of Be stars in young open clusters
- Short Name:
- J/AJ/155/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Through the modeling of near-infrared photometry of star-plus disk systems with the codes BEDISK/BERAY, we successfully describe the Wide-Field Infrared Survey Explorer (WISE) photometric characteristics of Be stars in five young open clusters, NGC 663, NGC 869, NGC 884, NGC 3766, and NGC 4755, broadly studied in the literature. WISE photometry allows previously known Be stars to be detected and to find new Be candidates which could be confirmed spectroscopically. The location of Be stars in the WISE color-magnitude diagram, separates them in two groups; active (Be stars hosting a developed circumstellar disk) and quiescent objects (Be stars in a diskless phase), and this way, we can explore how often stars are observed in these different stages. The variability observed in most active variable Be stars is compatible with a disk dissipation phase. We find that 50% of Be stars in the studied open clusters are in an active phase. We can interpret this as Be stars having a developed circumstellar disk one-half of the time. The location of Be stars with a developed disk in the color-magnitude diagram require mass loss rates in agreement with values recently reported in the literature. For these objects, we expect to have a tight relation between the equivalent width of the H{alpha} line and the mass of the disk, if the inclination is known. Also, near-infrared photometry of Be stars in stellar clusters has the potential of being useful to test whether there is a preferential viewing angle.
- ID:
- ivo://CDS.VizieR/J/AJ/148/51
- Title:
- WIYN Open Cluster. LXI. NGC 6819 photometry
- Short Name:
- J/AJ/148/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- NGC 6819 is a richly populated, older open cluster situated within the Kepler field. A CCD survey of the cluster on the uvbyCaH{beta} system, coupled with proper-motion membership, has been used to isolate 382 highly probable, single-star unevolved main-sequence members over a 20' field centered on the cluster. From 278 F dwarfs with high precision photometry in all indices, a mean reddening of E(b-y)=0.117+/-0.005 or E(B-V)=0.160+/-0.007 is derived, where the standard errors of the mean include both internal errors and the photometric zero-point uncertainty. With the reddening fixed, the metallicity derived from the same 278 stars is [Fe/H]=-0.116+/-0.101 from m_1_ and -0.055+/-0.033 from hk, for a weighted average of [Fe/H]=-0.06+/-0.04, where the quoted standard errors of the mean include the internal errors from the photometric scatter plus the uncertainty in the photometric zero points. If metallicity is derived using individual reddening values for each star to account for potential reddening variation across the face of the cluster, the analogous result is unchanged. The cluster members at the turnoff of the color-magnitude diagram are used to test and confirm the recently discovered variation in reddening across the face of the cluster, with a probable range in the variation of {Delta}E(B-V)=0.045+/-0.015. With the slightly higher reddening and lower [Fe/H] compared to commonly adopted values, isochrone fitting leads to an age of 2.3+/-0.2Gyr for an apparent modulus of (m-M)=12.40+/-0.12.
- ID:
- ivo://CDS.VizieR/J/AJ/148/61
- Title:
- WIYN open cluster study. LIX. RVs of NGC 6791
- Short Name:
- J/AJ/148/61
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The open cluster NGC 6791 has been the focus of much recent study due to its intriguing combination of old age and high metallicity (~8Gyr, [Fe/H]=+0.30), as well as its location within the Kepler field. As part of the WIYN Open Cluster Study, we present precise ({sigma}=0.38km/s) radial velocities for proper motion candidate members of NGC 6791 from Platais et al. Our survey, extending down to g' ~ 16.8, is comprised of the evolved cluster population, including blue stragglers, giants, and horizontal branch stars. Of the 280 proper-motion-selected stars above our magnitude limit, 93% have at least one radial velocity measurement and 79% have three measurements over the course of at least 200 days, sufficient for secure radial-velocity-determined membership of non-velocity-variable stars. The Platais et al. proper motion catalog includes 12 anomalous horizontal branch candidates blueward of the red clump, of which we find only 4 to be cluster members. Three fall slightly blueward of the red clump and the fourth is consistent with being a blue straggler. The cleaned color-magnitude diagram shows a richly populated red giant branch and a blue straggler population. Half of the blue stragglers are in binaries. From our radial velocity measurement distribution, we find the cluster's radial velocity dispersion to be {sigma}_c_=0.62+/-0.10km/s. This corresponds to a dynamical mass of ~4600M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/AJ/146/43
- Title:
- WIYN open cluster study. LV. NGC 6819
- Short Name:
- J/AJ/146/43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present proper motions and astrometric membership analysis for 15750 stars around the intermediate-age open cluster NGC 6819. The accuracy of relative proper motions for well-measured stars ranges from ~0.2mas/yr within 10' of the cluster center to 1.1mas/yr outside this radius. In the proper motion vector-point diagram, the separation between the cluster members and field stars is convincing down to V~18 and within 10' from the cluster center. The formal sum of membership probabilities indicates a total of ~2500 cluster members down to V~22. We confirm the cluster membership of several variable stars, including some eclipsing binaries. The estimated absolute proper motion of NGC 6819 is {mu}_x_^abs^=-2.6+/-0.5 and {mu}_y_^abs^=-4.2+/-0.5mas/yr. A cross-identification between the proper motion catalog and a list of X-ray sources in the field of NGC 6819 resulted in a number of new likely optical counterparts, including a candidate CV. For the first time we show that there is significant differential reddening toward NGC 6819.
- ID:
- ivo://CDS.VizieR/J/AJ/148/85
- Title:
- WIYN open cluster study. LXII. Photometry of M35
- Short Name:
- J/AJ/148/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The current generation of stellar isochrone models exhibits non-negligible discrepancies due to variations in the input physics. The success of each model is determined by how well it fits the observations, and this paper aims to disentangle contributions from the various physical inputs. New deep, wide-field optical and near-infrared photometry (UBVRIJHK_S_) of the cluster M35 is presented, against which several isochrone systems are compared: Padova, PARSEC, Dartmouth, and Y^2^. Two different atmosphere models are applied to each isochrone: ATLAS9 and BT-Settl. For any isochrone set and atmosphere model, observed data are accurately reproduced for all stars more massive than 0.7M_{sun}_. For stars less massive than 0.7M_{sun}_, Padova and PARSEC isochrones consistently produce higher temperatures than observed. Dartmouth and Y^2^ isochrones with BT-Settl atmospheres reproduce optical data accurately; however, they appear too blue in IR colors. It is speculated that molecular contributions to stellar spectra in the near-infrared may not be fully explored, and that future study may reconcile these differences.
- ID:
- ivo://CDS.VizieR/J/AJ/148/38
- Title:
- WIYN open cluster study. LX. RV survey of NGC 6819
- Short Name:
- J/AJ/148/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the current state of the WOCS radial-velocity (RV) survey for the rich open cluster NGC 6819 (2.5Gyr) including 93 spectroscopic binary orbits with periods ranging from 1.5 to 8000days. These results are the product of our ongoing RV survey of NGC 6819 using the Hydra Multi-Object Spectrograph on the WIYN 3.5m telescope. We also include a detailed analysis of multiple prior sets of optical photometry for NGC 6819. Within a 1{deg} field of view, our stellar sample includes the giant branch, the red clump, and blue straggler candidates, and extends to almost 2 mag below the main sequence (MS) turnoff. For each star observed in our survey we present all RV measurements, the average RV, and velocity variability information. Additionally, we discuss notable binaries from our sample, including eclipsing binaries (WOCS 23009, WOCS 24009, and WOCS 40007), stars noted in Kepler asteroseismology studies (WOCS 4008, WOCS 7009, and WOCS 8007), and potential descendants of past blue stragglers (WOCS 1006 and WOCS 6002). We find the incompleteness-corrected binary fraction for all MS binaries with periods less than 10^4^days to be 22%+/-3% and a tidal circularization period of 6.2^+1.1^_-1.1_days for NGC 6819.
