417 research outputs found
Morphology of luminous IRAS galaxies: Summary talk
The author discusses the morphology of luminous Infrared Astronomy Satellite (IRAS) galaxies. A few comments are made about the direction to be taken in future observations of luminous IRAS galaxies
Infrared observations of possible protostars
Energy distribution measurements on infrared objects located in H2 and gaseous nebulae region
Spitzer IRAC Observations of White Dwarfs. I. Warm Dust at Metal-Rich Degenerates
This paper presents the results of a Spitzer IRAC 3-8 micron photometric
search for warm dust orbiting 17 nearby, metal-rich white dwarfs, 15 of which
apparently have hydrogen dominated atmospheres (type DAZ). G166-58, G29-38, and
GD 362 manifest excess emission in their IRAC fluxes and the latter two are
known to harbor dust grains warm enough to radiate detectable emission at
near-infrared wavelengths as short as 2 micron. Their IRAC fluxes display
differences compatible with a relatively larger amount of cooler dust at GD
362. G166-58 is presently unique in that it appears to exhibit excess flux only
at wavelengths longer than about 5 micron. Evidence is presented that this
mid-infrared emission is most likely associated with the white dwarf,
indicating that G166-58 bears circumstellar dust no warmer than T~400 K. The
remaining 14 targets reveal no reliable mid-infrared excess, indicating the
majority of DAZ stars do not have warm debris disks sufficiently opaque to be
detected by IRAC.Comment: Accepted to ApJ, 10 figures, 6 table
Ground-based 1- to 32-microns observations of ARP 220: Evidence for a dust-embedded AGN?
New observations of the 10 and 20 micron size of the emission region in Arp 220 are presented. Also given are ground based photometry from 1 to 32 micron including measurements of the strength of the silicate feature at 10 micron. The results show that the 20 micron size of Arp is smaller than 1.5 arcsec (500 pc); comparison of IRAS and ground based observations show that IRAS 12 micron flux measured with a large arcmin beam is the same as that seen from the ground with a 3 arcsec aperture. At 10 micron a deep silicate absorption feature is seen that corresponds to a visual extinction of about 50 mag. These results suggest that a very significant portion of the 10 to the 12th power L sub 0 infrared luminosity from Arp 220 comes from a region less than or of the order of 500 pc in diameter. When these results are combined with recent measurement of a broad Brackett alpha line by DePoy and an unresolved 2.2 micron source by Neugebauer, Matthews and Scoville, a very attractive possibility for the primary luminosity source Arp 220 is a dust embedded compact Seyfert type nucleus
Optical and infrared spectrophotometry of 18 Markarian galaxies
Slit spectra, spectrophotometric scans and infrared broad band observations are presented. Eight of the program galaxies can be classified as Seyfert galaxies. Arguments are given that thermal, nonthermal and stellar radiation components were present. One group of Seyfert galaxies was characterized both by the presence of a high density region of gas and by a continuum dominated by nonthermal radiation. The continua of the remaining program Seyferts, which did not have a high density region of gas, were dominated by thermal radiation from dust and a stellar continuum. Ten of the galaxies, which are not Seyfert galaxies, are shown to be examples of extragalactic H 2 regions
Two-micron spectrophotometry of the galaxy NGC 253
A very strong Brackett-gamma hydrogen emission line, and the 2.3 micron CO stellar absorption feature were measured in NGC 253. The presence and strength of the CO feature indicates that late type giant stars produce most of the 2.2 micron continuum emission, while the rate of ionization implied by strength of the Brackett-gamma line indicates that much, perhaps all, of the luminosity detected at far infrared wavelengths originates from a large number of OB stars. As compared to the corresponding region of the Galaxy, the number of massive young stars in the central 200 pc of NGC 253 is thirty times greater, but the total mass of stars is roughly the same
Spitzer IRAC Observations of White Dwarfs. II. Massive Planetary and Cold Brown Dwarf Companions to Young and Old Degenerates
This paper presents a sensitive and comprehensive IRAC 3-8 m photometric
survey of white dwarfs for companions in the planetary mass regime with
temperatures cooler than the known T dwarfs. The search focuses on descendents
of intermediate mass stars with M\ga3 whose inner, few hundred AU
regions cannot be probed effectively for massive planets and brown dwarfs by
any alternative existing method. Furthermore, examination for mid-infrared
excess explores an extensive range of orbital semimajor axes, including the
intermediate 5-50 AU range poorly covered and incompletely accessible by other
techniques at main sequence or evolved stars. Three samples of white dwarfs are
chosen which together represent relatively young as well as older populations
of stars: 9 open cluster white dwarfs, 22 high mass field white dwarfs, and 17
metal-rich field white dwarfs. In particular, these targets include: 7 Hyads
and 4 field white dwarfs of similar age; 1 Pleiad and 19 field white dwarfs of
similar age; van Maanen 2 and 16 similarly metal-rich white dwarfs with ages
between 1 and 7 Gyr. No substellar companion candidates were identified at any
star. By demanding a 15% minimum photometric excess at 4.5 m to indicate a
companion detection, upper limits in the planetary mass regime are established
at 34 of the sample white dwarfs, 20 of which have limits below 10
according to substellar cooling models. Specifically, limits below the minimum
mass for deuterium burning are established at all Pleiades and Hyadeswhite
dwarfs, as well as similarly young field white dwarfs, half a dozen of which
receive limits at or below 5 . Two IRAC epochs at vMa 2 rule out
T\ga200 K proper motion companions within 1200 AU.Comment: 41 pages, accepted to Ap
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