- ID:
- ivo://CDS.VizieR/J/ApJ/452/210
- Title:
- UBV photometry in LH 47/48
- Short Name:
- J/ApJ/452/210
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the stellar population of an OB association, LH 47/48, which is associated with a superbubble H II region, DEM 152 in the N44 nebular complex of the Large Magellanic Cloud. With CCD photometry and spectroscopy of the massive stars, we find no evidence that an unusual stellar population gave rise to the shell morphology of the gas. The slope of the initial mass function, {Gamma}=1.3+/-0.2, is consistent with that of other OB associations in the LMC, and there is no significant difference in the initial mass function internal or external to the supershell. The inferred stellar ionizing flux is consistent with the observed nebular H alpha flux. We do find evidence for triggered star formation: the H-R diagram suggests an age of >10Myr for the population interior to the bubble with more recent, <5Myr, star formation on the exterior. Using the detailed data on the stellar population, we compare a numerical form of the Weaver et al. (1977ApJ...218..377W) evolutionary model for wind-driven bubbles with the observed shell kinematics. We find a substantial discrepancy: the observed shell radius is too small and/or expansion velocity too large to be explained with this version of the model. We discuss possible explanations for the inconsistency.
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1082. UBV photometry in M15
- ID:
- ivo://CDS.VizieR/J/AJ/124/3255
- Title:
- UBV photometry in M15
- Short Name:
- J/AJ/124/3255
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this series of two papers, we describe a project with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) to measure the line-of-sight velocities of stars in the central few arcseconds of the dense globular cluster M15. This first paper focuses on the observations and reduction of the data. We "scanned" the central region of M15 spectroscopically by consecutively placing the 0.1" HST/STIS slit at 18 adjacent positions. The spectral pixel size exceeds the velocity dispersion of M15. This puts the project at the limit of what is feasible with STIS, and exceedingly careful and complicated data reduction and analysis were required.
- ID:
- ivo://CDS.VizieR/J/PASP/83/800
- Title:
- UBV photometry in NGC 6025
- Short Name:
- J/PASP/83/800
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The table 1 lists photoelectric UBV measures for 78 stars in the open cluster NGC 6025. Distance and age estimates derived are 760pc and 100Myr. The brightest star, HD 143448, is a known emission star and is very probably a member of the cluster. Accurate positions and identifications of the stars were added by B. Skiff (Lowell Observatory) in November 2009.
- ID:
- ivo://CDS.VizieR/J/AJ/110/2715
- Title:
- UBV photometry in NGC 6822, M31 and M33
- Short Name:
- J/AJ/110/2715
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the massive star content of the three Local Group galaxies NGC 6822, M31, and M33 using crowded-field CCD UBV photometry in selected regions to identify the most luminous and massive stars. Optical spectroscopy is presented for many of these stars, allowing construction of accurate H-R diagrams and the first meaningful characterization of the massive star populations in these galaxies. The spectral types also allow investigation of the internal reddenings within these systems and provide fine candidates for stellar-wind studies in the UV. The early-type stars identified include O-type in all three systems, and we call attention to a new Luminous Blue Variable candidate in M33. Our spectroscopy of extreme B supergiants (M_V=-7.5) shows the expected changes with metallicity in comparison to similar objects in the Milky Way, LMC, and SMC, although the metal lines in the NGC 6822 stars are considerably weaker than that expected for a metallicity intermediate between that of the LMC and SMC, suggesting that this galaxy is more metal poor than usually supposed. There is considerable internal reddening within all three galaxies, including even the dwarf irregular NGC 6822, where the color excesses show a systematic spatial trend from E(B-V)=0.26 near the edges to 0.45 in the middle. The slope of the reddening curve is normal in NGC 6822 and M33, with E(U-B)/E(B-V)~0.72, but in M31 we find that this ratio is 0.4-0.5 in all three of our fields. We spectroscopically confirm that stars of high mass (>80M_{sun}_) and luminosity (Mbol~-11) are found in M31 and M33. We have not found stars of similar high mass or luminosity in NGC 6822, where the most luminous star present has Mbol=-10 and an inferred mass of 60M_{sun}_. Similarly, none of the OB associations in NGC 6822 are as impressive in terms of the number of massive stars as the rich associations of the Milky Way and Magellanic Clouds. However, OB78 (=NGC 206) and OB48 in M31 both contain 9-15 stars of mass >40M_{sun}_, making them comparable to impressive sites of star formation in the Milky Way and Magellanic Clouds. M33 contains regions that are even more extreme, with M33-OB127 and M33-OB21 containing 20-30 such stars. The low number of very massive stars in NGC 6822 is consistent with the overall star-formation rate inferred by other means, but the M33 results suggest that the formation of high-mass stars may be favored. The massive star content of individual associations would not have been inferred on the basis of Halpha flux, meaning that the nebulae associated with a number of these OB associations are density rather than radiation bounded, probably due to holes blown in the H I. We have also found that the ratio of the number of very massive (>40M_{sun}_) stars to the number of WR stars is constant within all the Local Group galaxies we have studied, suggesting that (a) the effect of metallicity on the evolution of massive stars is subtle if present, and (b) that WR stars make excellent tracers of the massive star populations. The fact that this ratio is roughly 3, rather than the 10 expected given the relative H- and He-burning lifetimes, argues that either our samples are (uniformly?) incomplete or that some fraction of WR stars are H-burning objects.
- ID:
- ivo://CDS.VizieR/J/A+A/361/945
- Title:
- UBV photometry in open cluster NGC 2539
- Short Name:
- J/A+A/361/945
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present UBV photoelectric observations of 345 stars in the field of the southern open cluster NGC 2539. The analysis of these data allows to determine that 169 stars are probable members of the cluster main sequence, while 23 are possible members.
1086. UBV photometry in RCW173
- ID:
- ivo://CDS.VizieR/J/A+A/534/A114
- Title:
- UBV photometry in RCW173
- Short Name:
- J/A+A/534/A114
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of several clusters of red supergiants towards l=24{deg}-30{deg} has triggered interest in this area of the Galactic plane, where lines of sight are very complex and previous explorations of the stellar content were very preliminary. We attempt to characterise the stellar population associated with the HII region RCW 173 (=Sh2-60), located at l=25.3{deg}, as previous studies have suggested that this population could be beyond the Sagittarius arm.
- ID:
- ivo://CDS.VizieR/J/AJ/130/1194
- Title:
- UBV photometry in Ruprecht 91
- Short Name:
- J/AJ/130/1194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric UBV photometry and star counts are presented for stars in the previously unstudied open cluster Ruprecht 91, supplemented by observations for stars in adjacent regions surrounding the Cepheids SX Car and VY Car, including new observations for the latter. Ruprecht 91 is typical of groups associated with Cepheids, with an evolutionary age of ~8x10^7^yr, but it is only 980+/-8pc distant, much closer than the Cepheids.
- ID:
- ivo://CDS.VizieR/J/AJ/73/772
- Title:
- UBV photometry in two LMC associations
- Short Name:
- J/AJ/73/772
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Photoelectric UBV observations were made in two associations in the Large Magellanic Cloud, in the magnitude range 10.6 to 16.2. The observations were made at the Cerro Tololo Inter-American Observatory with the 36-inch telescope in the nights of 1-5 December 1967. The positions were computed by B. Skiff (Lowell Obs.) in 2009.
1089. UBV photometry in W3
- ID:
- ivo://CDS.VizieR/J/AJ/129/393
- Title:
- UBV photometry in W3
- Short Name:
- J/AJ/129/393
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is generally believed that expanding superbubbles and mechanical feedback from massive stars trigger star formation, because there are numerous examples of superbubbles showing secondary star formation at their edges. However, although these systems show an age sequence, they do not provide strong evidence of a causal relationship. The W3/W4 Galactic star-forming complex suggests a three-generation hierarchy: the supergiant shell structures correspond to the oldest generation; these triggered the formation of IC 1795 in W3, the progenitor of a molecular superbubble that in turn triggered the current star-forming episodes in the embedded regions W3-North, W3-Main, and W3-OH. We present UBV photometry and spectroscopic classifications for IC 1795, which show an age of 3-5 Myr. This age is intermediate between the reported 6-20 Myr age of the supergiant shell system and the extremely young ages (10^4^-10^5^yr) for the embedded knots of the ultracompact HII regions, W3-North, W3-Main, and W3-OH. Thus, an age sequence is indeed confirmed for the entire W3/W4 hierarchical system. This therefore provides some of the first convincing evidence that superbubble action and mechanical feedback are indeed a triggering mechanism for star formation.
- ID:
- ivo://CDS.VizieR/J/AJ/102/642
- Title:
- UBV photometry in Westerlund 2
- Short Name:
- J/AJ/102/642
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Two new Galactic Wolf-Rayet stars were found in open clusters: a WN4 star in the O9 cluster Sher 1 and a WN7 star in the O7 cluster Westerlund 2. This confirms a previous trend, namely that fainter, hotter WN stars tend to be older than brighter, cooler WN stars. This may be a consequence of evolution via extreme mass loss.
