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MIPSGAL: A Survey of the Inner Galactic Plane at 24 and 70 μm
MIPSGAL is a 278 deg2 survey of the inner Galactic planeusing the Multiband Infrared Photometer for Spitzer aboard the SpitzerSpace Telescope. The survey field was imaged in two passbands, 24 and 70μm with resolutions of 6″ and 18″, respectively. Thesurvey was designed to provide a uniform, well-calibrated andwell-characterized data set for general inquiry of the inner Galacticplane and as a longer-wavelength complement to the shorter-wavelengthSpitzer survey of the Galactic plane: Galactic Plane Infrared MappingSurvey Extraordinaire. The primary science drivers of the current surveyare to identify all high-mass (M>5 Mȯ) protostars inthe inner Galactic disk and to probe the distribution, energetics, andproperties of interstellar dust in the Galactic disk. The observationswere planned to minimize data artifacts due to image latents at 24 μmand to provide full coverage at 70 μm. Observations at eclipticlatitudes within 15° of the ecliptic plane were taken at multipleepochs to help reject asteroids. The data for the survey were collectedin three epochs, 2005 September-October, 2006 April, and 2006 Octoberwith all of the data available to the public. The estimated point-sourcesensitivities of the survey are 2 and 75 mJy (3 σ) at 24 and 70μm, respectively. Additional data processing was needed to mitigateimage artifacts due to bright sources at 24 μm and detectorresponsivity variations at 70 μm due to the large dynamic range ofthe Galactic plane. Enhanced data products including artifact-mitigatedmosaics and point-source catalogs are being produced with the 24 μmmosaics already publicly available from the NASA/IPAC Infrared ScienceArchive. Some preliminary results using the enhanced data products aredescribed.
| Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope
The Infrared Array Camera (IRAC) on the Spitzer Space Telescope isabsolutely calibrated by comparing photometry of a set of A stars nearthe north ecliptic pole to predictions based on ground-basedobservations and a stellar atmosphere model. The brightness of pointsources is calibrated to an accuracy of 3%, relative to models forA-star stellar atmospheres, for observations performed and analyzed inthe same manner as for the calibration stars. This includes correctionsfor the location of the star in the array and the location of thecentroid within the peak pixel. Long-term stability of the IRACphotometry was measured by monitoring the brightness of A dwarfs and Kgiants (near the north ecliptic pole) observed several times per month;the photometry is stable to 1.5% (rms) over a year.Intermediate-timescale stability of the IRAC photometry was measured bymonitoring at least one secondary calibrator (near the ecliptic plane)every 12 hr while IRAC was in nominal operations; the intermediate-termphotometry is stable, with a 1% dispersion (rms). One of the secondarycalibrators was found to have significantly time-variable (5%)mid-infrared emission, with a period (7.4 days) matching the opticallight curve; it is possibly a Cepheid variable.
| IRAC Observations of Taurus Pre-Main-Sequence Stars
We present infrared photometry obtained with the IRAC camera on theSpitzer Space Telescope of a sample of 82 pre-main-sequence stars andbrown dwarfs in the Taurus star-forming region. We find a clearseparation in some IRAC color-color diagrams between objects with andwithout disks. A few ``transition'' objects are noted, which correspondto systems in which the inner disk has been evacuated of small dust.Separating pure disk systems from objects with remnant protostellarenvelopes is more difficult at IRAC wavelengths, especially for objectswith infall at low rates and large angular momenta. Our resultsgenerally confirm the IRAC color classification scheme used in previouspapers by Allen et al. and Megeath et al. to distinguish betweenprotostars, T Tauri stars with disks, and young stars without (inner)disks. The observed IRAC colors are in good agreement with recentimproved disk models, and in general accord with models for protostellarenvelopes derived from analyzing a larger wavelength region. We alsocomment on a few Taurus objects of special interest. Our results shouldbe useful for interpreting IRAC results in other, less well studiedstar-forming regions.
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| Takýmyýldýz: | Ejderha |
| Sað Açýklýk: | 19h12m47.20s |
| Yükselim: | +64°10'37.2" |
| Görünürdeki Parlaklýk: | 9.423 |
| özdevim Sað Açýklýk: | -2 |
| özdevim Yükselim: | -4.9 |
| B-T magnitude: | 9.609 |
| V-T magnitude: | 9.439 |
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