The range of V - R colors for a cluster of E and S0 galaxies as a function of redshift

The expected (V - R) color distribution for a centrally condensed, relaxed cluster of E and S0 galaxies has been calculated as a function of redshift. Because of the differences in the ultraviolet spectra of E and S0 galaxies, which are correlated with absolute magnitude, the spread in (V - R) colors for such a cluster becomes increasingly wide for increasing redshift. This effect becomes pronounced for redshifts of 0.4 and beyond. Thus evidence for the color evolution of cluster galaxies will be seen as an additional broadening of the color distribution

The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables Determined from Cluster Turn-offs. II. Results from 12 Galactic Clusters and OB Associations

Here we examine 12 Galactic clusters and OB associations containing Wolf-Rayet stars (W-Rs) and/or Luminous Blue Variables (LBVs), in order to assess the progentor masses of these evolved massive stars. We find that in the Milky Way, early-type WN stars evolve from stars with masses as low as 20Mo. Some early-type WN stars are found in clusters with very high turn-off masses, supporting our earlier results that the "WNE" class of W-Rs is a common stage in the evolution of stars with a wide range of mases. In contrast, the late-type WNs (particularly those of WN7 class) and the LBVs are only found in clusters with the very highest turn-off masses, suggesting that only the most massive stars evolve to these objects. An examination of the environment of the archetype LBV Eta Car reveals that this star is coeval with the rest of the Tr14/16 association, suggesting that its LBV properties is a normal consequence of evolution, and has little to do with the possibility that it is a binary.Comment: Scheduled for the Feb 2001 issue of the Astronomical Journal. Postscript version including figs from ftp://ftp.lowell.edu/pub/massey/galwr.ps.g

The star formation history of Trumpler 14 and Trumpler 16

H-R diagrams are presented for the very young galactic clusters Trumpler 14 and Trumpler 16, which are the two most populous clusters in the region of vigorous star formation surrounding η Carinae. Point spread function photometry of UBV CCD images is presented down to V~19 for over 560 stars in Tr 16 and 290 stars in Tr 14. We have also obtained similar data for a local background field. After determining cluster membership through proper motions from a previous work, we find that the reddening of cluster members is significantly lower than that of the local background stars. Thus, we are able to use individual reddenings to identify likely members at far deeper levels than possible with proper motions. This work has revealed a significant population of pre-main-sequence (PMS) stars in both clusters. The location of the PMS stars in the H-R diagram indicates that the theoretical ``stellar birthline'' of Palla & Stahler follows the locus of stars far better than that of Beech & Mitalas. Comparison with both pre- and post-main-sequence isochrones also reveals that although intermediate-mass stars have been forming continuously over the last 10 Myr, the high-mass stars formed within the last 3 Myr. There is no evidence that the formation of the intermediate-mass stars was truncated by the formation of the high-mass stars

A correlation between infrared excess and period for Mira variables

The [8.7]-[11.4] infrared color is found to increase monotonically with increasing period for a sample of 41 Mira variables. We conclude that mass loss is not a stochastic process and that for any Mira variable the rate of mass loss is directly linked to the parameters which dictate the period of that variable

Massive star formation in NGC 6946

H-alpha measurements of the late-type spiral galaxy NGC 6946 are presented. Assuming an initial mass function, the H-alpha data are used to calculate the total star formation rate and efficiency of massive star formation as a function of galactocentric radius. An attempt is made to determine the factors influencing these quantities by comparing them to the surface densities of H I and H 2 and the degree of compression suffered by the gas in spiral density wave theory. The rate of star formation is very closely correlated with the first power of the surface density of H2, and somewhat less correlated with the degree of compression of the gas predicted by density wave theory. In contrast, the efficiency of massive star formation is roughly constant across the face of the galaxy

Young Brown Dwarfs in the Core of the W3 Main Star-Forming Region

We present the results of deep and high-resolution (FWHM ~ 0".35) JHK NIR observations with the Subaru telescope, to search for very low mass young stellar objects (YSOs) in the W3 Main star-forming region. The NIR survey covers an area of ~ 2.6 arcmin^2 with 10-sigma limiting magnitude exceeding 20 mag in the JHK bands. The survey is sensitive enough to provide unprecedented details in W3 IRS 5 region and reveals a census of the stellar population down to objects below the hydrogen-burning limit. We construct JHK color-color (CC) and J-H/J and H-K/K color-magnitude (CM) diagrams to identify very low luminosity YSOs and to estimate their masses. Based on these CC and CM diagrams, we identified a rich population of embedded YSO candidates with infrared excesses (Class I and Class II), associated with the W3 Main region. A large number of red sources (H-K > 2) have also been detected around W3 Main. We argue that these red stars are most probably pre-main-sequence (PMS) stars with intrinsic color excesses. Based on the comparison between theoretical evolutionary models of very low-mass PMS objects with the observed CM diagram, we find there exists a substantial substellar population in the observed region. The mass function (MF) does not show the presence of cutoff and sharp turnover around the substellar limit, at least at the hydrogen-burning limit. Furthermore, the MF slope indicates that the number ratio of young brown dwarfs and hydrogen-burning stars in the W3 Main is probably higher than those in Trapezium and IC 348. The presence of mass segregation, in the sense that relatively massive YSOs lie near the cluster center, is seen. The estimated dynamical evolution time indicates that the observed mass segregation in the W3 Main may be the imprint of the star formation process.Comment: 39 pages, 15 figures. Accepted for publication in the Astrophysical Journa

The Giant Pillars of the Carina Nebula

Results are presented from a multi-wavelength study of the giant pillars within the Carina Nebula. Using near-IR data from 2MASS, mid-IR data from MSX, 843MHz radio continuum maps from the MOST, and molecular line and continuum observations from the SEST, we investigate the nature of the pillars and search for evidence of ongoing star formation within them. Photodissociation regions (PDRs) exist across the whole nebula and trace the giant pillars, as well as many ridges, filaments, and condensations (Av > 7 mag). Morphological similarities between emission features at 21um and 843MHz adjacent to the PDRs, suggests that the molecular material has been carved by the intense stellar winds and UV radiation from the nearby massive stars. In addition, star forming cores are found at the tips of several of the pillars. Using a stellar density distribution, several candidate embedded clusters are also found. One is clearly seen in the 2MASS images and is located within a dense core (G287.84-0.82). A search for massive young stellar objects and compact HII regions using mid-IR colour criteria, reveal twelve candidates across the complex. Grey-body fits to SEDs for four of these objects are suggestive of OB-stars. We find that massive star formation in the Carina Nebula is occurring across the whole complex and confirm it has been continuous over the past 3 Myrs.Comment: 14 pages, 10 figures (low resolution), accepted by A&

Global X-ray properties of the O and B stars in Carina

The key empirical property of the X-ray emission from O stars is a strong correlation between the bolometric and X-ray luminosities. In the framework of the Chandra Carina Complex Project, 129 O and B stars have been detected as X-ray sources; 78 of those, all with spectral type earlier than B3, have enough counts for at least a rough X-ray spectral characterization. This leads to an estimate of the Lx/Lbol ratio for an exceptional number of 60 O stars belonging to the same region and triples the number of Carina massive stars studied spectroscopically in X-rays. The derived log(Lx/Lbol) is -7.26 for single objects, with a dispersion of only 0.21dex. Using the properties of hot massive stars listed in the literature, we compare the X-ray luminosities of different types of objects. In the case of O stars, the Lx/Lbol ratios are similar for bright and faint objects, as well as for stars of different luminosity classes or spectral types. Binaries appear only slightly harder and slightly more luminous in X-rays than single objects; the differences are not formally significant (at the 1% level), except for the Lx/Lbol ratio in the medium (1.0--2.5keV) energy band. Weak-wind objects have similar X-ray luminosities but they display slightly softer spectra compared to "normal" O stars with the same bolometric luminosity. Discarding three overluminous objects, we find a very shallow trend of harder emission in brighter objects. The properties of the few B stars bright enough to yield some spectral information appear to be different overall (constant X-ray luminosities, harder spectra), hinting that another mechanism for producing X-rays, besides wind shocks, might be at work. However, it must be stressed that the earliest and X-ray brightest amongst these few detected objects are similar to the latest O stars, suggesting a possibly smooth transition between the two processes.Comment: 30 pages, 9 figures. Accepted for the ApJS Special Issue on the Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special Issue papers are available at http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at leas

Candidate X-ray-Emitting OB Stars in the Carina Nebula Identified Via Infrared Spectral Energy Distributions

We report the results of a new survey of massive, OB stars throughout the Carina Nebula using the X-ray point source catalog provided by the Chandra Carina Complex Project (CCCP) in conjunction with infrared (IR) photometry from the Two Micron All-Sky Survey and the Spitzer Space Telescope Vela--Carina survey. Mid-IR photometry is relatively unaffected by extinction, hence it provides strong constraints on the luminosities of OB stars, assuming that their association with the Carina Nebula, and hence their distance, is confirmed. We fit model stellar atmospheres to the optical (UBV) and IR spectral energy distributions (SEDs) of 182 OB stars with known spectral types and measure the bolometric luminosity and extinction for each star. We find that the extinction law measured toward the OB stars has two components: Av=1--1.5 mag produced by foreground dust with a ratio of total-to-selective absorption Rv=3.1 plus a contribution from local dust with Rv>4.0 in the Carina molecular clouds that increases as Av increases. Using X-ray emission as a strong indicator of association with Carina, we identify 94 candidate OB stars with Lbol\geq10^4 Lsun by fitting their IR SEDs. If the candidate OB stars are eventually confirmed by follow-up spectroscopic observations, the number of cataloged OB stars in the Carina Nebula will increase by ~50%. Correcting for incompleteness due to OB stars falling below the Lbol cutoff or the CCCP detection limit, these results potentially double the size of the young massive stellar population.Comment: 19 pages, 8 figures, accepted for the ApJS Special Issue on the Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special Issue papers, including a version of this article with high-quality figures, are available at http://cochise.astro.psu.edu/Carina_public/special_issue.html (through 2011 at least

A Catalog of Chandra X-ray Sources in the Carina Nebula

We present a catalog of ~14,000 X-ray sources observed by the ACIS instrument on the Chandra X-ray Observatory within a 1.42 square degree survey of the Great Nebula in Carina, known as the Chandra Carina Complex Project (CCCP). This study appears in a Special Issue of the ApJS devoted to the CCCP. Here, we describe the data reduction and analysis procedures performed on the X-ray observations, including calibration and cleaning of the X-ray event data, point source detection, and source extraction. The catalog appears to be complete across most of the field to an absorption-corrected total-band luminosity of ~10^{30.7} erg/s for a typical low-mass pre-main sequence star. Counterparts to the X-ray sources are identified in a variety of visual, near-infrared, and mid-infrared surveys. The X-ray and infrared source properties presented here form the basis of many CCCP studies of the young stellar populations in Carina.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special Issue papers are available at http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at least. 29 pages, 11 figure