Modeling Spitzer observations of VV Ser. II. an extended quantum heated nebula and a disk shadow

We present mid-infrared Spitzer IRAC and MIPS images of the UX Orionis star VV Ser and the surrounding cloud. The 5.6--70 micron images show bright, localized and nebulous emission extended over 4 arcmin centered on VV Ser. We interpret the nebulosity as being due to transiently heated grains excited by UV photons emitted by VV Ser. A companion paper describes how the physical structure of the VV Ser disk has been constrained using a wide range of observational data modeled by an axisymmetric Monte Carlo radiative transfer code. In this paper we employ the model to study the nebulosity surrounding VV Ser using quantum-heated PAH molecules and Very Small Grains (VSGs) consisting of amorphous carbon in the thermal cooling approximation. Imprinted on the nebulosity is a wedge-shaped dark band, centered on the star. We interpret this dark wedge as the shadow cast by the inner regions of a near-edge-on disk in UV light, allowing the PAHs to be excited only outside of this shadow. The presence of a disk shadow strongly constrains the inclination as well as the position angle of the disk. Although depending on the adopted PAH opacity, the abundance of PAHs in the surrounding cloud is constrained to 5+/-2% of the total dust mass, given the opacity. The extent of the nebulosity constrains the density of the gas surrounding the VV Ser disk to 500+/-200 cm-3 for a gas-to-dust ratio of 100. This low density suggests that the quantum heated material is not part of the original envelope of VV Ser and that it is rather a quiescent part of the Serpens molecular cloud that the star has passed into after being formed. [Abstract abridged

The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. I. Chamaeleon II Observed with MIPS

We present maps of over 1.5 square degrees in Chamaeleon (Cha) II at 24, 70, and 160 micron observed with the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS) and a 1.2 square degree millimeter map from SIMBA on the Swedish-ESO Submillimetre Telescope (SEST). The c2d Spitzer Legacy Team's data reduction pipeline is described in detail. Over 1500 24 micron sources and 41 70 micron sources were detected by MIPS with fluxes greater than 10-sigma. More than 40 potential YSOs are identified with a MIPS and 2MASS color-color diagram and by their spectral indices, including two previously unknown sources with 24 micron excesses. Our new SIMBA millimeter map of Cha II shows that only a small fraction of the gas is in compact structures with high column densities. The extended emission seen by MIPS is compared with previous CO observations. Some selected interesting sources, including two detected at 1 mm, associated with Cha II are discussed in detail and their SEDs presented. The classification of these sources using MIPS data is found to be consistent with previous studies.Comment: 44 pages, 12 figures (1 color), to be published in Ap

The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. VIII. Serpens Observed with MIPS

We present maps of 1.5 deg^2 of the Serpens dark cloud at 24, 70, and 160 μm observed with the Spitzer Space Telescope MIPS camera. We describe the observations and briefly discuss the data processing carried out by the c2d team on these data. More than 2400 compact sources have been extracted at 24 μm, nearly 100 at 70 μm, and four at 160 μm. We estimate completeness limits for our 24 μm survey from Monte Carlo tests with artificial sources inserted into the Spitzer maps. We compare source counts, colors, and magnitudes in the Serpens cloud to two reference data sets: a 0.50 deg^2 set on a low-extinction region near the dark cloud, and a 5.3 deg^2 subset of the SWIRE ELAIS N1 data that was processed through our pipeline. These results show that there is an easily identifiable population of young stellar object candidates in the Serpens cloud that is not present in either of the reference data sets. We also show a comparison of visual extinction and cool dust emission illustrating a close correlation between the two and find that the most embedded YSO candidates are located in the areas of highest visual extinction

An estimate of the time variation of the O/H radial gradient from planetary nebulae

Radial abundance gradients are a common feature of spiral galaxies, and in the case of the Galaxy both the magnitude of the gradients and their variations are among the most important constraints of chemical evolution models. Planetary nebulae (PN) are particularly interesting objects to study the gradients and their variations. Owing to their bright emission spectra, they can be observed even at large galactocentric distances, and the derived abundances are relatively accurate, with uncertainties of about 0.1 to 0.2 dex, particularly for the elements that are not synthesized in their progenitor stars. On the other hand, as the offspring of intermediate mass stars, with main sequence masses in the interval of 1 to 8 solar masses, they are representative of objects with a reasonable age span. In this paper, we present an estimate of the time variation of the O/H radial gradient in a sample containing over 200 nebulae with accurate abundances. Our results are consistent with a flattening of the O/H gradient roughly from -0.11 dex/kpc to -0.06 dex/kpc during the last 9 Gyr, or from -0.08 dex/kpc to -0.06 dex/kpc during the last 5 Gyr.Comment: 9 pages, 7 encapsulated postscript figures, LaTeX, uses Astronomy and Astrophysics macro aa.cls, graphicx package, to be published in Astronomy and Astrophysics (2002), Also available at: http://www.astro.iag.usp.br/~macie

Early Galactic Evolution of Carbon, Nitrogen and Oxygen

We present results on carbon, nitrogen, and oxygen abundances for a sample of unevolved metal-poor stars with metallicities in the range -0.3< [Fe/H]< -3. Oxygen abundances derived from different indicators are compared showing consistently that in the range 0.3 >[Fe/H]>-3.0, the [O/Fe] ratio increases from approximately 0 to 1. We find a good agreement between abundances based on the forbidden line, the OH and IR triplet lines when gravities based on Hipparcos} parallaxes are considered for the sample stars. Gravities derived from LTE ionization balance in metal-poor stars with [Fe/H]< -1 are likely too low, and could be responsible for an underestimation of the oxygen abundances derived using the [OI] line. [C/Fe] and [N/Fe] ratios appear to be constant, independently of metallicity, in the same range. However, they show larger scatter than oxygen at a given metallicity, which could reflect the larger variety of stellar production sites for these other elements.Comment: 10 pages, 3 figures, To appear in the proceedings of the conference "The Chemical Evolution of The Milky Way: Stars versus Clusters", eds. F. Matteucci and F. Giovannelli, Vulcano, Italy, September 20-24 199

The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. VII. Ophiuchus Observed with MIPS

We present maps of 14.4 deg^2 of the Ophiuchus dark clouds observed by the Spitzer Space Telescope Multiband Imaging Photometer for Spitzer (MIPS). These high-quality maps depict both numerous point sources and extended dust emission within the star-forming and non–star-forming portions of these clouds. Using PSF-fitting photometry, we detect 5779 sources at 24 μm and 81 sources at 70 μm at the 10 σ level of significance. Three hundred twenty-three candidate young stellar objects (YSOs) were identified according to their positions on the MIPS/2MASS K versus color-magnitude diagrams, as compared to 24 μm detections in the SWIRE extragalactic survey. We find that more than half of the YSO candidates, and almost all those with protostellar Class I spectral energy distributions, are confined to the known cluster and aggregates

Empirically Constrained Color-Temperature Relations. II. uvby

(Abriged) A new grid of theoretical color indices for the Stromgren uvby photometric system has been derived from MARCS model atmospheres and SSG synthetic spectra for cool dwarf and giant stars. At warmer temperatures this grid has been supplemented with the synthetic uvby colors from recent Kurucz atmospheric models without overshooting. Our transformations appear to reproduce the observed colors of extremely metal-poor turnoff and giant stars (i.e., [Fe/H]<-2). Due to a number of assumptions made in the synthetic color calculations, however, our color-temperature relations for cool stars fail to provide a suitable match to the uvby photometry of both cluster and field stars having [Fe/H]>-2. To overcome this problem, the theoretical indices at intermediate and high metallicities have been corrected using a set of color calibrations based on field stars having accurate IRFM temperature estimates and spectroscopic [Fe/H] values. Encouragingly, isochrones that employ the transformations derived in this study are able to reproduce the observed CMDs (involving u-v, v-b, and b-y colors) for a number of open and globular clusters (including M92, M67, the Hyades, and 47Tuc) rather well. Moreover, our interpretations of such data are very similar, if not identical, with those given by VandenBerg & Clem (2003, AJ, 126, 778) from a consideration of BV(RI)c observations for the same clusters. In the present investigation, we have also analyzed the observed Stromgren photometry for the classic Population II subdwarfs, compared our "final" (b-y)-Teff relationship with those derived empirically in a number of recent studies, and examined in some detail the dependence of the m1 index on [Fe/H].Comment: 70 pages, 26 figures. Accepted for publication in AJ (Feb 2004). Postscript version with high resolution figures and complete Table 3 available at http://astrowww.phys.uvic.ca/~jclem/uvb

The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. IV. Lupus Observed with MIPS

We present maps of 7.78 square degrees of the Lupus molecular cloud complex at 24, 70, and $160\:\mu$m. They were made with the Spitzer Space Telescope's Multiband Imaging Photometer for Spitzer (MIPS) instrument as part of the Spitzer Legacy Program, ``From Molecular Cores to Planet-Forming Disks'' (c2d). The maps cover three separate regions in Lupus, denoted I, III, and IV. We discuss the c2d pipeline and how our data processing differs from it. We compare source counts in the three regions with two other data sets and predicted star counts from the Wainscoat model. This comparison shows the contribution from background galaxies in Lupus I. We also create two color magnitude diagrams using the 2MASS and MIPS data. From these results, we can identify background galaxies and distinguish them from probable young stellar objects. The sources in our catalogs are classified based on their spectral energy distribution (SED) from 2MASS and Spitzer wavelengths to create a sample of young stellar object candidates. From 2MASS data, we create extinction maps for each region and note a strong corresponence between the extinction and the $160\:\mu$m emission. The masses we derived in each Lupus cloud from our extinction maps are compared to masses estimated from $^{13}$CO and C$^{18}$O and found to be similar to our extinction masses in some regions, but significantly different in others. Finally, based on our color-magnitude diagrams, we selected 12 of our reddest candidate young stellar objects for individual discussion. Five of the 12 appear to be newly-discovered YSOs.Comment: 15 pages, 17 figures, uses emulateapj.cls. Accepted for publication in ApJ. A version with high-quality figures can be found at http://peggysue.as.utexas.edu/SIRTF