T. N. Gautier

THE INFRARED ASTRONOMICAL SATELLITE (IRAS) MISSION

The Infrared Astronomical Satellite (IRAS) consists of a spacecraft and a liquid helium cryostat that contains a cooled IR telescope. The telescopes focal plane assembly is cooled to less than 3 K, and contains 62 IR detectors in the survey array which are arranged so that every source crossing the field of view can be seen by at least two detectors in each of four wavelength bands. The satellite was launched into a 900 km-altitude near-polar orbit, and its cryogenic helium supply was exhausted on November 22, 1983. By missions end, 72 percent of the sky had been observed with three or more hours-confirming scans, and 95 percent with two or more hours-confirming scans. About 2000 stars detected at 12 and 25 microns early in the mission, and identified in the SAO (1966) catalog, have a positional uncertainty ellipse whose axes are 45 x 9 arcsec for an hours-confirmed source.

Infrared cirrus - New components of the extended infrared emission

Extended sources of far-infrared emission superposed on the zodiacal and galactic backgrounds are found at high galactic latitudes and near the ecliptic plane. Clouds of interstellar dust at color temperatures as high as 35 K account for much of this complex structure, but the relationship to H I column density is not simple. Other features of the extended emission show the existence of warm structures within the solar system. Three bands of dust clouds at temperatures of 150-200 K appear within 10 deg on both sides of the ecliptic plane. Their ecliptic latitudes and derived distances suggest that they are associated with the main asteroid belt. A third component of the 100-micron cirrus, poorly correlated with H I, may represent cold material in the outer solar system or a new component of the interstellar medium.

New Debris Disks Around Nearby Main Sequence Stars: Impact on The Direct Detection of Planets

Using the MIPS instrument on Spitzer, we have searched for infrared excesses around a sample of 82 stars, mostly F, G, and K main-sequence field stars, along with a small number of nearby M stars. These stars were selected for their suitability for future observations by a variety of planet-finding techniques. These observations provide information on the asteroidal and cometary material orbiting these stars, data that can be correlated with any planets that may eventually be found. We have found significant excess 70 μm emission toward 12 stars. Combined with an earlier study, we find an overall 70 μm excess detection rate of 13% ± 3% for mature cool stars. Unlike the trend for planets to be found preferentially toward stars with high metallicity, the incidence of debris disks is uncorrelated with metallicity. By newly identifying four of these stars as having weak 24 μm excesses (fluxes ~10% above the stellar photosphere), we confirm a trend found in earlier studies wherein a weak 24 μm excess is associated with a strong 70 μm excess. Interestingly, we find no evidence for debris disks around 23 stars cooler than K1, a result that is bolstered by a lack of excess around any of the 38 K1-M6 stars in two companion surveys. One motivation for this study is the fact that strong zodiacal emission can make it hard or impossible to detect planets directly with future observatories such as the Terrestrial Planet Finder (TPF). The observations reported here exclude a few stars with very high levels of emission, >1000 times the emission of our zodiacal cloud, from direct planet searches. For the remainder of the sample, we set relatively high limits on dust emission from asteroid belt counterparts.

IRAS OBSERVATIONS OF THE DIFFUSE INFRARED BACKGROUND

IRAS data reveal bright emission from interplanetary dust which dominates the celestial background at 12, 25, and 60 microns except near the galactic plane. At 100 microns, interplanetary dust emission is prominent only near the ecliptic plane; diffuse galactic emission is found over the rest of the sky. At the galactic poles, the observed brightness implies that A(v) is likely to be of order 0.1 mag. The angular variation of the zodiacal emission in the ecliptic plane and in the plane at elongation 90 deg, and an annual modulation of the ecliptic pole brightness, are generally consistent with previously determined interplanetary dust distributions.

On the Relative Sizes of Planets within Kepler Multiple-candidate Systems

We present a study of the relative sizes of planets within the multiple-candidate systems discovered with the Kepler mission. We have compared the size of each planet to the size of every other planet within a given planetary system after correcting the sample for detection and geometric biases. We find that for planet pairs for which one or both objects are approximately Neptune-sized or larger, the larger planet is most often the planet with the longer period. No such size-location correlation is seen for pairs of planets when both planets are smaller than Neptune. Specifically, if at least one planet in a planet pair has a radius of ≳ 3 R_⊕, 68% ± 6% of the planet pairs have the inner planet smaller than the outer planet, while no preferred sequential ordering of the planets is observed if both planets in a pair are smaller than ≾ 3 R_⊕.

Caltech Faint Galaxy Redshift Survey. IX. Source Detection and Photometry in the Hubble Deep Field Region

Detection and photometry of sources in the U_n, G, ℛ, and K_s bands in a 9 × 9 arcmin^2 region of the sky, centered on the Hubble Deep Field, are described. The data permit construction of complete photometric catalogs to roughly U_n = 25, G = 26, ℛ = 25.5, K_s = 20 mag and significant photometric measurements somewhat fainter. The galaxy number density is 1.3 × 10^5 deg^(-2) to ℛ = 25.0 mag. Galaxy number counts have slopes d log N/dm = 0.42, 0.33, 0.27, and 0.31 in the U_n, G, ℛ, and K_s bands, consistent with previous studies and the trend that fainter galaxies are, on average, bluer. Galaxy catalogs selected in the ℛ and K_s bands are presented, containing 3607 and 488 sources in field areas of 74.8 and 59.4 arcmin^2, to ℛ = 25.5 and K_s = 20 mag.

IRAS Observations of the Interplanetary Dust Emission

The Infrared Astronomical Satellite (IRAS) has completed a sensitive, highly redundant survey of the full sky in four broad photometric bands at 12, 25, 60, and 100 micrometers wavelength. The survey measured interplanetary dust emission over elongation angles ranging from 60 to 120 degrees. Bright emission from the main cloud is consistent with optically thin blackbody emission. The grains are evidently quite black, with an “apparent albedo” of about 0.07. The data show clear evidence for deviation of the dust symmetry surface from the ecliptic plane. Surprising bands of emission were discovered near the ecliptic plane and about ten degrees on either side of it. The heliocentric distance of this material, suggested to be asteroidal in origin, is inferred to be about 2.5 AU from both color temperature and parallax measurements.

The formation of solar type stars - IRAS observations of the dark cloud Barnard 5

Observations of the dark cloud Barnard 5 show two compact sources of radiation within the dense core. IRS 1 is associated with 30-800 K dust, has a total luminosity of about 10 L, and is presumably a newly formed star of rougly solar mass. IRS 2 has a much cooler color temperature, approximately 25 K, and emits only 1.3 L. Its status is unclear, but IRS 2 may be at a very early stage of gravitational within the cloud heated by the interstellar radiation field. Also within the confines of the cloud are two point sources, which, if associated with the cloud, each emit about 0.5 L in the IRAS bands. These may be T Tauri stars, separated from the cloud but still enshrouded in dust shells.

IRAS images of the galactic center

Some preliminary IRAS results in the form of images at 12, 25, 60, and 100 microns of an 8 deg x 15 deg area around the galactic center are presented. These absolute intensity maps have unprecedented sensitivity combined with high angular resolution, wide field coverage, and large wavelength range. They give a broad view of the central galaxy revealing previously unseen details, especially in regions far from the central few arcmin. Well-defined infrared features in the nucleus correspond to the nuclear radio sources Sgr A, B2, C, and D. Extremely faint structures are detected, such as the cold molecular cloud associated with Sgr B2 which has never before been detected at wavelenths shorter than 40 microns.

A CATALOG OF BRIGHT FILAMENTARY STRUCTURES IN THE INTERSTELLAR MEDIUM

We present a listing of prominent filamentary structures in the interstellar cirrus, selected with an eye toward current and planned far-infrared and submillimeter polarimetry facilities. The filaments were identified on the 100 μm plates of the IRAS Sky Survey Atlas (ISSA), using a computer vision algorithm that is unbiased with respect to source intensity. Our catalog is two-tiered: the selection criteria in the Galactic plane are based on the sensitivity limits of airborne polarimeters such as the proposed HALE instrument for SOFIA, and away from the plane the limits are dictated by the sensitivities of balloon-borne cosmic microwave background experiments, such as BOOMERanG and MAXIMA. Infrared detector technology is currently at the point where detecting the polarization of the interstellar cirrus is feasible, and we hope this catalog will assist any experimenter undertaking this task.