Browsing by Subject "infrared array camera"
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Item Converting From 3.6 And 4.5 Micron Fluxes To Stellar Mass(2012-06) Eskew, Michael; Zaritsky, Dennis; Meidt, Sharon; Eskew, MichaelWe use high spatial resolution maps of stellar mass and infrared flux of the Large Magellanic Cloud (LMC) to calibrate a conversion between 3.6 and 4.5 mu m fluxes and stellar mass, M-* = 10(5.65) F-3.6(2.85) F-4.5(-1.85) (D/0.05)(2) M-circle dot,where fluxes are in Jy and D is the luminosity distance to the source in Mpc, and to provide an approximate empirical estimate of the fractional internal uncertainty in M* of 0.3 root N/10(6), where N is the number of stars in the region. We find evidence that young stars and hot dust contaminate the measurements, but attempts to remove this contamination using data that are far superior to what are generally available for unresolved galaxies resulted in marginal gains in accuracy. The scatter among mass estimates for regions in the LMC is comparable to that found by previous investigators when modeling composite populations, and so we conclude that our simple conversion is as precise as possible for the data and models currently available. Our results allow for a reasonably bottom-heavy initial mass function, such as Salpeter or heavier, and moderately disfavor lighter versions such as a diet-Salpeter or Chabrier initial mass function.Item The Spitzer Gould Belt Survey of Large Nearby Interstellar Clouds: Discovery of A Dense Embedded Cluster in the Serpens-Aquila Rift(2008-02) Gutermuth, R. A.; Bourke, Tyler L.; Allen, L. E.; Myers, Philip C.; Megeath, S. T.; Matthews, B. C.; Jorgensen, J. K.; Di Francesco, J.; Ward-Thompson, D.; Huard, Tracy L.; Brooke, T. Y.; Dunham, Miranda M.; Cieza, Lucas A.; Harvey, Paul M.; Chapman, N. L.; Dunham, Miranda M.; Cieza, Lucas A.; Harvey, Paul M.We report the discovery of a nearby, embedded cluster of young stellar objects, associated filamentary infrared dark cloud, and 4.5 mu m shock emission knots from outflows detected in Spitzer IRAC mid-infrared imaging of the Serpens-Aquila Rift obtained as part of the Spitzer Gould Belt Legacy Survey. We also present radial velocity measurements of the region from molecular line observations obtained with the Submillimeter Array (SMA) that suggest the cluster is comoving with the Serpens Main embedded cluster to the north. We therefore assign it 3 degrees the same distance, 260 pc. The core of the new cluster, which we call Serpens South, is composed of an unusually large fraction of protostars (77%) at high mean surface density (> 430 pc(-2)) and short median nearest neighbor spacing (3700 AU). We perform basic cluster structure characterization using nearest neighbor surface density mapping of the YSOs and compare our findings to other known clusters with equivalent analyses available in the literature.Item The Spitzer Survey of Interstellar Clouds in the Gould Belt. II. the Cepheus Flare Observed With IRAC and MIPS(2009-11) Kirk, Jason M.; Ward-Thompson, Derek; Di Francesco, James; Bourke, Tyler L.; Evans, Neal J., II; Merin, Bruno; Allen, Lori E.; Cieza, Lucas A.; Dunham, Michael M.; Harvey, Paul; Huard, Tracy; Jorgensen, Jes K.; Miller, Jennifer F.; Noriega-Crespo, Alberto; Peterson, Dawn; Ray, Tom P.; Rebull, Luisa M.; Dunham, Michael M.; Harvey, PaulWe present Spitzer Infrared Array Camera (IRAC; similar to 2 deg(2)) and Multiband Imaging Photometer for Spitzer (MIPS; similar to 8 deg(2)) observations of the Cepheus Flare, which is associated with the Gould Belt, at an approximate distance of similar to 300 pc. Around 6500 sources are detected in all four IRAC bands, of which similar to 900 have MIPS 24 mu m detections. We identify 133 young stellar object (YSO) candidates using color-magnitude diagram techniques, and a large number of the YSO candidates are associated with the NGC 7023 reflection nebula. Cross-identifications were made with the Guide Star Catalog II and the IRAS Faint Source Catalog, and spectral energy distributions (SEDs) were constructed. SED modeling was conducted to estimate the degree of infrared excess. It was found that a large majority of disks were optically thick accreting disks, suggesting that there has been little disk evolution in these sources. Nearest neighbor clustering analysis identified four small protostellar groups (L1228, L1228N, L1251A, and L1251B) with 5-15 members each and the larger NGC 7023 association with 32 YSO members. The star-Formation efficiency for cores with clusters of protostars and for those without clusters was found to be similar to 8% and similar to 1%, respectively. The cores L1155, L1241, and L1247 are confirmed to be starless down to our luminosity limit of L(bol) = 0.06 L(circle dot).Item Star Formation In Perseus V. Outflows Detected By HARP(2009-07) Hatchell, J.; Dunham, M. M.; Dunham, M. M.Aims. Molecular outflows provide an alternative method of identifying protostellar cores, complementary to recent mid-infrared studies. Continuing our studies of Perseus, we investigate whether all Spitzer-identified protostars, and particularly those with low luminosities, drive outflows and if any new protostellar cores (perhaps harbouring low-mass sources) can be identified via their outflows alone. Methods. We have used the heterodyne array receiver HARP on JCMT to make deep (12)CO 3-2 maps of submm cores in Perseus, extending and deepening our earlier study with RxB and bringing the total number of SCUBA cores studied up to 83. Our survey includes 23/25 of the Spitzer low-luminosity objects believed to be embedded protostars, including three VeLLOs. Results. All but one of the cores identified as harbouring embedded YSOs have outflows, confirming outflow detections as a good method for identifying protostars. We detect outflows from 20 Spitzer low-luminosity objects. We do not conclusively detect any outflows from IR-quiet cores, though confusion in clustered regions such as NGC1333 makes it impossible to identify all the individual driving sources. This similarity in detection rates despite the difference in search methods and detection limits suggests either that the sample of protostars in Perseus is now complete or that the existence of an outflow contributes to the Spitzer detectability, perhaps through the contribution of shocked H(2) emission in the IRAC bands. For five of the low-luminosity sources (including two previously believed to be embedded), there is no protostellar envelope detected at 350 mu m and the Spitzer emission is entirely due to shocks. Additionally, we detect the outflow from IRAS 03282+3035 at 850 mu m with SCUBA with 20-30% of the submm flux due to CO line contamination in the continuum passband.