- ID:
- ivo://CDS.VizieR/J/AJ/122/3219
- Title:
- M3 and M13 CCD BV photometry
- Short Name:
- J/AJ/122/3219
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-precision V, B-V color-magnitude diagrams (CMDs) for the classic second-parameter globular clusters M3 and M13 from wide-field, deep CCD photometry. The data for the two clusters were obtained during the same photometric nights with the same instrument, allowing us to determine accurate relative ages. Based on a differential comparison of the CMDs using the {Delta}(B-V) method, an age difference of 1.7+/-0.7Gyr is obtained between these two clusters. We compare this result with our updated horizontal-branch (HB) population models, which confirm that the observed age difference can produce the difference in HB morphology between the clusters. This provides further evidence that age is the dominant second parameter that influences HB morphology.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/131/2478
- Title:
- M31 and M33 UBVRI photometry
- Short Name:
- J/AJ/131/2478
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the Kitt Peak National Observatory 4m telescope. We describe our data reduction and automated photometry techniques in some detail, as we will shortly perform a similar analysis of other Local Group galaxies. The present study covered 2.2deg^2^ along the major axis of M31 and 0.8deg^2^ on M33, chosen so as to include all of the regions currently active in forming massive stars. We calibrated our data using photometry from the Lowell 1.1m telescope, and this external method resulted in millimagnitude differences in the photometry of overlapping fields, providing some assurance that our photometry is reliable. The final catalog contains 371781 and 146622 stars in M31 and M33, respectively, where every star has a counterpart in (at least) the B, V, and R passbands. Our survey goes deep enough to achieve 1%-2% photometry at 21mag (corresponding to stars more massive than 20M_{sun}_) and achieves <10% errors at ~U ~B ~V ~R ~I 23mag.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/101
- Title:
- Massive field OB stars in the SMC
- Short Name:
- J/ApJ/763/101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Some theories of star formation suggest massive stars may only form in clustered environments, which would create a deficit of massive stars in low-density environments. Observationally, Massey (2002, Cat. II/236) finds such a deficit in samples of the field population in the Small and Large Magellanic Clouds, with an initial mass function (IMF) slope of {Gamma}_IMF_~4. These IMF measurements represent some of the largest known deviations from the standard Salpeter IMF slope of {Gamma}_IMF_=1.35. Here, we carry out a comprehensive investigation of the mass function above 20M_{sun}_ for the entire field population of the Small Magellanic Cloud (SMC), based on data from the Runaways and Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). This is a spatially complete census of the entire field OB star population of the SMC obtained with the IMACS multi-object spectrograph and MIKE echelle spectrograph on the Magellan telescopes. Based on Monte Carlo simulations of the evolved present-day mass function, we find the slope of the field IMF above 20M_{sun}_ is {Gamma}_IMF_=2.3+/-0.4. We extend our IMF measurement to lower masses using BV photometry from the OGLE II survey. We use a statistical approach to generate a probability distribution for the mass of each star from the OGLE photometry, and we again find {Gamma}_IMF_=2.3+/-0.6 for stellar masses from 7M_{sun}_ to 20M_{sun}_. The discovery and removal of ten runaways in our RIOTS4 sample steepens the field IMF slope to {Gamma}_IMF_=2.8+/-0.5. We discuss the possible effects of binarity and star formation history on our results, and conclude that the steep field massive star IMF is most likely a real effect.
- ID:
- ivo://CDS.VizieR/J/AJ/101/1408
- Title:
- Massive stars in Cyg OB2.
- Short Name:
- J/AJ/101/1408
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The galactic association Cygnus OB2, which contains heavily reddened O and B stars, has been studied using CCD UBV photometry and spectroscopy. The file "mt91.dat" contains precise coordinates, UBV photometry, and spectral types from the study of Cygnus OB2, and merges the tables 2, 5 and 6 from the paper.
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/3765
- Title:
- Mass-loss rates in LMC and SMC O stars
- Short Name:
- J/MNRAS/470/3765
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a combination of BVJHK and Spitzer [3.6], [5.8] and [8.0] photometry to determine infrared (IR) excesses for a sample of 58 Large Magellanic Cloud and 46 Small Magellanic Cloud O stars. This sample is ideal for determining IR excesses because the very small line-of-sight reddening minimizes uncertainties due to extinction corrections. We use the core-halo model developed by Lamers & Waters to translate the excesses into mass-loss rates and demonstrate that the results of this simple model agree with the more sophisticated CMFGEN models to within a factor of 2. Taken at face value, the derived mass-loss rates are larger than those predicted by Vink et al. (2001A&A...369..574V), and the magnitude of the disagreement increases with decreasing luminosity. However, the IR excesses need not imply large mass-loss rates. Instead, we argue that they probably indicate that the outer atmospheres of O stars contain complex structures and that their winds are launched with much smaller velocity gradients than normally assumed. If this is the case, it could affect the theoretical and observational interpretations of the 'weak wind' problem, where classical mass-loss indicators suggest that the mass-loss rates of lower luminosity O stars are far less than expected.
- ID:
- ivo://CDS.VizieR/J/ApJ/753/71
- Title:
- Mass-loss return from LMC evolved stars. VI.
- Short Name:
- J/ApJ/753/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to ~30000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry.
897. M 4 CCD photometry
- ID:
- ivo://CDS.VizieR/J/AJ/114/189
- Title:
- M 4 CCD photometry
- Short Name:
- J/AJ/114/189
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the ESO NTT, we have obtained accurate CCD UBVI photometry of 1649 stars in an extended field in the globular cluster M 4 = NGC 6121. The position of the main-sequence turnoff is found to be at V_TO_=17.0+/-0.1mag, (B-V)=0.863+/-0.007, (V-I)=1.224+/-0.010, (B-I)=2.084+/-0.010. Our turnoff point is redder and fainter than those found for M 4 in the majority of recent studies, probably because of our field being located in the western, most reddened part of the cluster. The spread of stars around the main-sequence locus has an unusual shape (broadening near the turnoff point and close to the photometric limit), earlier noticed by Richer et al. (1995ApJ...451L..17R) and attributed by them to photometric effects. We have analyzed the possible reasons for this effect and concluded that, at least in our case, it is most probably due to differential absorption. We confirm the deviation of theoretical isochrones from the fainter parts of the M 4 main-sequence locus found by Alcaino et al. (1988ApJ...330..569A). Several curious structural details (a depression and an excess of stars) have been revealed in the brighter parts of the main-sequence luminosity function of M 4.
- ID:
- ivo://CDS.VizieR/J/AJ/145/106
- Title:
- M31 Cepheid disk sample of 1st year of PS1
- Short Name:
- J/AJ/145/106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a sample of Cepheid variable stars towards M31 based on the first year of regular M31 observations of the PS1 survey in the r_P1 and i_P1 filters. We describe the selection procedure for Cepheid variable stars from the overall variable source sample and develop an automatic classification scheme using Fourier decomposition and the location of the instability strip. We find 1440 fundamental mode (classical {delta}) Cep stars, 126 Cepheids in the first overtone mode, and 147 belonging to the Population II types. 296 Cepheids could not be assigned to one of these classes and 354 Cepheids were found in other surveys. These 2009 Cepheids constitute the largest Cepheid sample in M31 known so far and the full catalog is presented in this paper. We briefly describe the properties of our sample in its spatial distribution throughout the M31 galaxy, in its age properties, and we derive an apparent period-luminosity relation (PLR) in our two bands. The Population I Cepheids nicely follow the dust pattern of the M31 disk, whereas the 147 Type II Cepheids are distributed throughout the halo of M31. We outline the time evolution of the star formation in the major ring found previously and find an age gradient. A comparison of our PLR to previous results indicates a curvature term in the PLR.
- ID:
- ivo://CDS.VizieR/J/ApJS/91/583
- Title:
- MC massive stars IMF. I.
- Short Name:
- J/ApJS/91/583
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- UBV CCD photometry has been obtained for 14 OB associations in the Magellanic Clouds using the University of Toronto's 0.6m telescope and the Carnegie Institution of Washington's 1.0m reflector, both on Las Campanas, Chile. The data are presented and used to construct color-magnitude diagrams for the purposes of investigating the massive-star content of the associations.
- ID:
- ivo://CDS.VizieR/J/AJ/132/2187
- Title:
- MCT1 photometry of NGC 5128 globular clusters
- Short Name:
- J/AJ/132/2187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first results from an imaging program with the ACS on the Hubble Space Telescope designed to measure the structural characteristics of a wide range of globular clusters in NGC 5128, the nearest giant elliptical galaxy. From 12 ACS WFC fields we have measured a total of 62 previously known globular clusters and have discovered 69 new high-probability cluster candidates not found in any previous work. We present magnitudes and color indices for all of these, along with rough measurements of their effective diameters and ellipticities.
