Stephan D. Price

The Two Micron All Sky Survey (2MASS)

Between 1997 June and 2001 February the Two Micron All Sky Survey (2MASS) collected 25.4 Tbytes of raw imagingdatacovering99.998%ofthecelestialsphereinthenear-infraredJ(1.25 � m),H(1.65 � m),andKs(2.16 � m) bandpasses. Observations were conducted from two dedicated 1.3 m diameter telescopes located at Mount Hopkins, Arizona,andCerroTololo,Chile.The7.8sofintegrationtimeaccumulatedforeachpointontheskyandstrictquality control yielded a 10 � point-source detection level of better than 15.8, 15.1, and 14.3 mag at the J, H, and Ks bands, respectively, for virtually the entire sky. Bright source extractions have 1 � photometric uncertainty of <0.03 mag and astrometric accuracy of order 100 mas. Calibration offsets between any two points in the sky are <0.02 mag. The 2MASS All-Sky Data Release includes 4.1 million compressed FITS images covering the entire sky, 471 million source extractions in a Point Source Catalog, and 1.6 million objects identified as extended in an Extended Source Catalog.

The Supplemental IRAS Minor Planet Survey

We present additional and revised IRAS diameters and albedos for the 1992 IRAS Minor Planet Survey (IMPS). Using orbital elements for 26,791 numbered asteroids, we found 2228 different multiply observed asteroids associated with IRAS sources, an increase of 432 (24%) over IMPS. The IRAS sample of small asteroids, diameters D < 20.0 km, has increased by 72% (from 306 to 526), the sample of Jupiter Trojan asteroids by 77% (from 39 to 69), and the sample of small Trojan asteroids (D < 80 km) by nearly a factor of 3 (from nine to 26). We present the entire Supplemental IRAS Minor Planet Survey data set, describe how it was created, compare it with the IMPS data set, and estimate how many more asteroids remain to be found in the IRAS data.

A Population of Cold Cores in the Galactic Plane

Recent observations by the Midcourse Space Experiment (MSX) have revealed the presence of compact objects seen in absorption against bright mid-infrared emission from the Galactic plane. Examination of MSX and IRAS images of these objects reveal that they are dark from 7 to 100 μm. We find ~2000 clouds in a 1° × 180° scan along the Galactic equator. The data suggest these objects are dense (n > 105 cm−3), cold (T<20 K) cores, without accompanying envelopes.

The Physical Properties of the Midcourse Space Experiment Galactic Infrared-dark Clouds

The SPIRIT III infrared telescope on the Midcourse Space Experiment (MSX) satellite has provided an unprecedented view of the mid-infrared emission (8-25 μm) of the Galactic plane. An initial analysis of images from MSX Galactic plane survey data reveals dark clouds seen in silhouette against the bright emission from the Galactic plane (Egan et al.). These clouds have mid-infrared extinctions in excess of 2 mag at 8 μm. We probed the physical properties of 10 of these MSX dark clouds using millimeter-wave molecular rotational lines as an indicator of dense molecular gas. All 10 clouds were detected in millimeter spectral lines of H2CO, which confirms the presence of dense gas. The distances to these clouds range from 1 to 8 kiloparsecs and their diameters from 0.4 to 15.0 pc. Excitation analysis of the observed lines indicates that the clouds are cold (T 105 cm-3]. Some of the clouds have nearby H II regions, H2O masers, and other tracers of star formation at comparable spectral line velocities; however, only one cloud contains embedded centimeter or infrared sources. The lack of mid- to far-infrared emission associated with these clouds suggests that they are not currently forming high-mass stars. If star formation is present in these clouds, it is clearly protostellar class 0 or earlier.

A Uniform Database of 2.4-45.4 Micron Spectra from the Infrared Space Observatory Short Wavelength Spectrometer*

We present a complete set of all valid SWS full-scan 2.4-45.4 μm spectra processed and renormalized in as uniform a manner as possible. The processing produces a single spectrum for each observation from the 288 individual spectral segments, which are the most processed form available from the ISO archive. The spectra, and the programs used to create them, are available to the community on-line.

Submillimeter Observations of Midcourse Space Experiment Galactic Infrared-Dark Clouds

We present 850 and 450 μm continuum images of infrared-dark clouds (IRDCs) taken with the Submillimeter Common-User Bolometer Array (SCUBA) submillimeter camera at the James Clerk Maxwell Telescope. The IRDCs are large (1-10 pc diameter) molecular cores with gas densities ~106 cm-3 and temperatures ≈15 K. We detected strong submillimeter sources with peak flux densities of ≈1 Jy beam-1 at 850 μm in all eight clouds that were observed. The submillimeter emission generally lies within the envelope of the mid-infrared extinction where dense gas has been detected using H2CO as a tracer. The dust temperatures in the bright, compact sources are calculated to lie in the range 10-25 K. The masses of these sources are estimated to be in the range of several tens up to about a thousand solar masses. The corresponding gas column densities range over an order of magnitude, up to about 1023 cm-2. Several of the sources are detected in emission at both 850 and 8 μm. Two of the sources have HCO+ line profiles characteristic of molecular infall. It is likely that the bright, compact sources seen in the SCUBA images are in various early stages of star formation, from preprotostellar cores to class I objects.

Large-Scale Structure of the Carina Nebula

Observations obtained with the Midcourse Space Experiment (MSX) satellite reveal for the first time the complex mid-infrared morphology of the entire Carina Nebula (NGC 3372). On the largest size scale of approximately 100 pc, the thermal infrared emission from the giant H ii region delineates one coherent structure: a (somewhat distorted) bipolar nebula with the major axis perpendicular to the Galactic plane. The Carina Nebula is usually described as an evolved H ii region that is no longer actively forming stars, clearing away the last vestiges of its natal molecular cloud. However, the MSX observations presented here reveal numerous embedded infrared sources that are good candidates for sites of current star formation. Several compact infrared sources are located at the heads of dust pillars or in dark globules behind ionization fronts. Because their morphology suggests a strong interaction with the peculiar collection of massive stars in the nebula, we speculate that these new infrared sources may be sites of triggered star formation in NGC 3372.

Guilt by Association: The 13 Micron Dust Emission Feature and Its Correlation to Other Gas and Dust Features*

A study of all full-scan spectra of optically thin oxygen-rich circumstellar dust shells in the database produced by the Short Wavelength Spectrometer on ISO reveals that the strength of several infrared spectral features correlates with the strength of the 13 ?m dust feature. These correlated features include dust features at 19.8 and 28.1 ?m and the bands produced by warm carbon dioxide molecules (the strongest of which are at 13.9, 15.0, and 16.2 ?m). The database does not provide any evidence for a correlation of the 13 ?m feature with a dust feature at 32 ?m, and it is more likely that a weak emission feature at 16.8 ?m arises from carbon dioxide gas rather than dust. The correlated dust features at 13, 20, and 28 ?m tend to be stronger with respect to the total dust emission in semiregular and irregular variables associated with the asymptotic giant branch than in Mira variables or supergiants. This family of dust features also tends to be stronger in systems with lower infrared excesses and thus lower mass-loss rates. We hypothesize that the dust features arise from crystalline forms of alumina (13 ?m) and silicates (20 and 28 ?m).

Mid-Infrared Spectroscopy of Carbon Stars in the Small Magellanic Cloud

We have observed a sample of 36 objects in the Small Magellanic Cloud (SMC) with the Infrared Spectrometer on the Spitzer Space Telescope. Nineteen of these sources are carbon stars. An examination of the near- and mid-infrared photometry shows that the carbon-rich and oxygen-rich dust sources follow two easily separated sequences. A comparison of the spectra of the 19 carbon stars in the SMC to spectra from the Infrared Space Observatory (ISO) of carbon stars in the Galaxy reveals significant differences. The absorption bands at 7.5 and 13.7 μm due to C2H2 are stronger in the SMC sample, and the SiC dust emission feature at 11.3 μm is weaker. Our measurements of the MgS dust emission feature at 26-30 μm are less conclusive, but this feature appears to be weaker in the SMC sample as well. All of these results are consistent with the lower metallicity in the SMC. The lower abundance of SiC grains in the SMC may result in less efficient carbon-rich dust production, which could explain the excess C2H2 gas seen in the spectra. The sources in the SMC with the strongest SiC dust emission tend to have redder infrared colors than the other sources in the sample, which implies more amorphous carbon, and they also tend to show stronger MgS dust emission. The weakest SiC emission features tend to be shifted to the blue; these spectra may arise from low-density shells with large SiC grains.

Tracking a major interplanetary disturbance with SMEI

[1] We present the first clear observations of an Earth-directed interplanetary disturbance tracked by the Solar Mass Ejection Imager (SMEI). We find that this event can be related to two halo CMEs seen at the Sun about 2 days earlier, and which merged in transit to 1 AU. The disturbance was seen about 16 hours before it reached Earth, and caused a severe geomagnetic storm at the time which would have been predicted had SMEI been operating as a real-time monitor. It is concluded that SMEI is capable of giving many hours advance warning of the possible arrival of interplanetary disturbances.