arXiv subjects

Brian M. Patten

Publications and source records attributed to Brian M. Patten.

8 recordsLinked to original sources

arXiv2011

The Spitzer Survey of Interstellar Clouds in the Gould Belt. III. A Multi-Wavelength View of Corona Australis

We present Spitzer Space Telescope IRAC and MIPS observations of a 0.85 deg^2 field including the Corona Australis (CrA) star-forming region. At a distance of 130 pc, CrA is one of the closest regions known to be actively forming stars, particularly within its embedded association, the Coronet. Using the Spitzer data, we identify 51 young stellar objects (YSOs) in CrA which include sources in the well-studied Coronet cluster as well as distributed throughout the molecular cloud. Twelve of the YSOs discussed are new candidates, one of which is located in the Coronet. Known YSOs retrieved from the literature are also added to the list, and a total of 116 candidate YSOs in CrA are compiled. Based on these YSO candidates, the star formation rate is computed to be 12 M_o Myr^-1, similar to that of the Lupus clouds. A clustering analysis was also performed, finding that the main cluster core, consisting of 68 members, is elongated (having an aspect ratio of 2.36), with a circular radius of 0.59 pc and mean surface density of 150 pc^-2. In addition, we analyze outflows and jets in CrA by means of new CO and H_2 data. We present 1.3 mm interferometric continuum observations made with the Submillimeter Array (SMA) covering R CrA, IRS 5, IRS 7, and IRAS 18595-3712 (IRAS 32). We also present multi-epoch H_2 maps and detect jets and outflows, study their proper motions, and identify exciting sources. The Spitzer and ISAAC/VLT observations of IRAS 32 show a bipolar precessing jet, which drives a CO (2-1) outflow detected in the SMA observations. There is also clear evidence for a parsec-scale precessing outflow, E-W oriented, and originating in the SMA 2 region, likely driven by SMA 2 or IRS 7A.

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arXiv2009

An Infrared Census of Star Formation in the Horsehead Nebula

At ~ 400 pc, the Horsehead Nebula (B33) is the closest radiatively-sculpted pillar to the Sun, but the state and extent of star formation in this structure is not well understood. We present deep near-infrared (IRSF/SIRIUS JHKs) and mid-infrared (Spitzer/IRAC) observations of the Horsehead Nebula in order to characterize the star forming properties of this region and to assess the likelihood of triggered star formation. Infrared color-color and color-magnitude diagrams are used to identify young stars based on infrared excess emission and positions to the right of the Zero-Age Main Sequence, respectively. Of the 45 sources detected at both near- and mid-infrared wavelengths, three bona fide and five candidate young stars are identified in this 7' by 7' region. Two bona fide young stars have flat infrared SEDs and are located at the western irradiated tip of the pillar. The spatial coincidence of the protostars at the leading edge of this elephant trunk is consistent with the Radiation-Driven Implosion (RDI) model of triggered star formation. There is no evidence, however, for sequential star formation within the immediate ~ 1.5' (0.17 pc) region from the cloud/H II region interface.

astro-ph.SR↗

arXiv2007

Far Infrared Prperties of M Dwarfs

We report the mid- and far-infrared properties of nearby M dwarfs. Spitzer/MIPS measurements were obtained for a sample of 62 stars at 24 um, with subsamples of 41 and 20 stars observed at 70 um and 160 um respectively. We compare the results with current models of M star photospheres and look for indications of circumstellar dust in the form of significant deviations of K-[24 um] colors and 70 um / 24 um flux ratios from the average M star values. At 24 um, all 62 of the targets were detected; 70 um detections were achieved for 20 targets in the subsample observed; and no detections were seen in the 160 um subsample. No clear far-infrared excesses were detected in our sample. The average far infrared excess relative to the photospheric emission of the M stars is at least four times smaller than the similar average for a sample of solar-type stars. However, this limit allows the average fractional infrared luminosity in the M-star sample to be similar to that for more massive stars. We have also set low limits for the maximum mass of dust possible around our stars.

astro-ph↗

arXiv2007

Near and Mid-IR Photometry of the Pleiades, and a New List of Substellar Candidate Members

We make use of new near and mid-IR photometry of the Pleiades cluster in order to help identify proposed cluster members. We also use the new photometry with previously published photometry to define the single-star main sequence locus at the age of the Pleiades in a variety of color-magnitude planes. The new near and mid-IR photometry extend effectively two magnitudes deeper than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new set of candidate very low mass and sub-stellar mass members of the Pleiades in the central square degree of the cluster. We identify 42 new candidate members fainter than Ks =14 (corresponding to 0.1 Mo). These candidate members should eventually allow a better estimate of the cluster mass function to be made down to of order 0.04 solar masses. We also use new IRAC data, in particular the images obtained at 8 um, in order to comment briefly on interstellar dust in and near the Pleiades. We confirm, as expected, that -- with one exception -- a sample of low mass stars recently identified as having 24 um excesses due to debris disks do not have significant excesses at IRAC wavelengths. However, evidence is also presented that several of the Pleiades high mass stars are found to be impacting with local condensations of the molecular cloud that is passing through the Pleiades at the current epoch.

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arXiv2006

Identification of the Microlens in Event MACHO-LMC-20

We report on the identification of the lens responsible for microlensing event MACHO-LMC-20. As part of a \textit{Spitzer}/IRAC program conducting mid-infrared follow-up of the MACHO Large Magellanic Cloud microlensing fields, we discovered a significant flux excess at the position of the source star for this event. These data, in combination with high resolution near-infrared \textit{Magellan}/PANIC data has allowed us to classify the lens as an early M dwarf in the thick disk of the Milky Way, at a distance of $\sim 2$ kpc. This is only the second microlens to have been identified, the first also being a M dwarf star in the disk. Together, these two events are still consistent with the expected frequency of nearby stars in the Milky Way thin and thick disks acting as lenses.

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arXiv2006

The effects of cosmic rays and solar flares on the IRAC detectors: the first two years of in-flight operation

The Infrared Array Camera (IRAC) is a four-channel camera on the Spitzer Space Telescope, one of three focal plane science instruments. IRAC uses two pairs of 256x256 pixel InSb and Si:As IBC detectors to provide simultaneous imaging at 3.6, 4.5, 5.8, and 8 microns. IRAC experiences a flux of cosmic rays and solar protons that produce transient effects in science images from each of the arrays, with 4-6 pixels per second being affected during each integration. During extreme solar flares, IRAC experiences a much higher rate of transients which affects the science data quality. We present cosmic ray rates and observed detector characteristics for IRAC during the first two years of science operation, and rates observed in a period of elevated solar proton flux during an intense solar flare in January 2005. We show the changes to the IRAC detectors observed since launch, and assess their impacts to the science data quality.

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arXiv2006

Spitzer/IRAC Photometry of M, L, and T Dwarfs

We present the results of a program to acquire photometry for eighty-six late-M, L, and T dwarfs using the Infrared Array Camera (IRAC) on the Spitzer Space Telescope. We examine the behavior of these cool dwarfs in various color-color and color-magnitude diagrams composed of near-IR and IRAC data. The T dwarfs exhibit the most distinctive positions in these diagrams. In M_5.8 versus [5.8]-[8.0], the IRAC data for T dwarfs are not monotonic in either magnitude or color, giving the clearest indication yet that the T dwarfs are not a one parameter family in Teff. Because metallicity does not vary enough in the solar neighborhood to act as the second parameter, the most likely candidate then is gravity, which in turn translates to mass. Among objects with similar spectral type, the range of mass suggested by our sample is about a factor of five (~70 M_Jup to ~15 M_Jup), with the less massive objects making up the younger members of the sample. We also find the IRAC 4.5 micron fluxes to be lower than expected, from which we infer a stronger CO fundamental band at ~4.67 microns. This suggests that equilibrium CH_4/CO chemistry underestimates the abundance of CO in T dwarf atmospheres, confirming earlier results based on M-band observations from the ground. In combining IRAC photometry with near-IR JHK photometry and parallax data, we find the combination of Ks, IRAC 3.6 micron, and 4.5 micron bands to provide the best color-color discrimination for a wide range of M, L, and T dwarfs. Also noteworthy is the M_Ks versus Ks-[4.5] relation, which shows a smooth progression over spectral type and splits the M, L, and T types cleanly.

astro-ph↗

arXiv2005

SWAS observations of comet 9P/Tempel 1 and Deep Impact

On 4 July 2005 at 1:52 UT the Deep Impact mission successfully completed its goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on the nucleus and ejecting material into the coma of the comet. The 370 kg impactor collided with the sunlit side of the nucleus with a relative velocity of 10.2 km/s. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the 1(10)-1(01) ortho-water ground-state rotational transition in comet 9P/Tempel 1 before, during, and after the impact. No excess emission from the impact was detected by SWAS. However, the water production rate of the comet showed large natural variations of more than a factor of three during the weeks before the impact.

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