52 research outputs found
The Low Velocity Wind from the Circumstellar Matter Around the B9V Star sigma Herculis
We have obtained FUSE spectra of sigma Her, a nearby binary system, with a
main sequence primary, that has a Vega-like infrared excess. We observe
absorption in the excited fine structure lines C II* at 1037 A, N II* at 1085
A, and N II** at 1086 A that are blueshifted by as much as ~30 km/sec with
respect to the star. Since these features are considerably narrower than the
stellar lines and broader than interstellar features, the C II and N II are
circumstellar. We suggest that there is a radiatively driven wind, arising from
the circumstellar matter, rather than accretion as occurs around beta Pic,
because of sigma Her's high luminosity. Assuming that the gas is liberated by
collisions between parent bodies at 20 AU, the approximate distance at which
blackbody grains are in radiative equilibrium with the star and at which 3-body
orbits become unstable, we infer dM/dt ~ 6 * 10^-12 M_{sun}/yr. This wind
depletes the minimum mass of parent bodies in less than the estimated age of
the system.Comment: 6 pages, 3 figures, ApJ in pres
Radii of 88 M subdwarfs and updated radius relations for low-metallicity M-dwarf stars
M subdwarfs are low-metallicity M dwarfs that typically inhabit the halo population of the Galaxy. Metallicity controls the opacity of stellar atmospheres; in metal-poor stars, hydrostatic equilibrium is reached at a smaller radius, leading to smaller radii for a given effective temperature. We compile a sample of 88 stars that span spectral classes K7 to M6 and include stars with metallicity classes from solar-metallicity dwarf stars to the lowest metallicity ultra subdwarfs to test how metallicity changes the stellar radius. We fit models to Palomar Double Spectrograph (DBSP) optical spectra to derive effective temperatures (T_ eff) and we measure bolometric luminosities (L_ bol) by combining broad wavelength-coverage photometry with Gaia parallaxes. Radii are then computed by combining the T_ eff and L_ bol using the StefanâBoltzman law. We find that for a given temperature, ultra subdwarfs can be as much as five times smaller than their solar-metallicity counterparts. We present color-radius and color-surface brightness relations that extend down to [Fe/H] of â2.0 dex, in order to aid the radius determination of M subdwarfs, which will be especially important for the WFIRST exoplanetary microlensing survey.Published versio
The infrared spectrograph on the Spitzer Space Telescope
The Infrared Spectrograph (IRS) is one of three science instruments on the Spitzer Space Telescope. The IRS comprises four separate spectrograph modules covering the wavelength range from 5.3 to 38 Îźm with spectral resolutions, R~90 and 650, and it was optimized to take full advantage of the very low background in the space environment. The IRS is performing at or better than the pre-launch predictions. An autonomous target acquisition capability enables the IRS to locate the mid-infrared centroid of a source, providing the information so that the spacecraft can accurately offset that centroid to a selected slit. This feature is particularly useful when taking spectra of sources with poorly known coordinates. An automated data reduction pipeline has been developed at the Spitzer Science Center
The AllWISE Motion Survey, Part 2
We use the AllWISE Data Release to continue our search for WISE-detected
motions. In this paper, we publish another 27,846 motion objects, bringing the
total number to 48,000 when objects found during our original AllWISE motion
survey are included. We use this list, along with the lists of confirmed
WISE-based motion objects from the recent papers by Luhman and by Schneider et
al. and candidate motion objects from the recent paper by Gagne et al. to
search for widely separated, common-proper-motion systems. We identify 1,039
such candidate systems. All 48,000 objects are further analyzed using
color-color and color-mag plots to provide possible characterizations prior to
spectroscopic follow-up. We present spectra of 172 of these, supplemented with
new spectra of 23 comparison objects from the literature, and provide
classifications and physical interpretations of interesting sources. Highlights
include: (1) the identification of three G/K dwarfs that can be used as
standard candles to study clumpiness and grain size in nearby molecular clouds
because these objects are currently moving behind the clouds, (2) the
confirmation/discovery of several M, L, and T dwarfs and one white dwarf whose
spectrophotometric distance estimates place them 5-20 pc from the Sun, (3) the
suggestion that the Na 'D' line be used as a diagnostic tool for interpreting
and classifying metal-poor late-M and L dwarfs, (4) the recognition of a triple
system including a carbon dwarf and late-M subdwarf, for which model fits of
the late-M subdwarf (giving [Fe/H] ~ -1.0) provide a measured metallicity for
the carbon star, and (5) a possible 24-pc-distant K5 dwarf + peculiar red L5
system with an apparent physical separation of 0.1 pc.Comment: 62 pages with 80 figures, accepted for publication in The
Astrophysical Journal Supplement Series, 23 Mar 2016; second version fixes a
few small typos and corrects the footnotes for Table
Observations of Ultraluminous Infrared Galaxies with the Infrared Spectrograph on the Spitzer Space Telescope: Early Results on Mrk 1014, Mrk 463, and UGC 5101
We present spectra taken with the Infrared Spectrograph on Spitzer covering
the 5-38micron region of three Ultraluminous Infrared Galaxies (ULIRGs): Mrk
1014 (z=0.163), and Mrk 463 (z=0.051), and UGC 5101 (z=0.039). The continua of
UGC 5101 and Mrk 463 show strong silicate absorption suggesting significant
optical depths to the nuclei at 10microns. UGC 5101 also shows the clear
presence of water ice in absorption. PAH emission features are seen in both Mrk
1014 and UGC 5101, including the 16.4micron line in UGC 5101. The fine
structure lines are consistent with dominant AGN power sources in both Mrk 1014
and Mrk 463. In UGC 5101 we detect the [NeV] 14.3micron emission line providing
the first direct evidence for a buried AGN in the mid-infrared. The detection
of the 9.66micron and 17.03micron H emission lines in both UGC 5101 and
Mrk 463 suggest that the warm molecular gas accounts for 22% and 48% of the
total molecular gas masses in these galaxies.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 3 figure
Structure and Colors of Diffuse Emission in the Spitzer Galactic First Look Survey
We investigate the density structure of the interstellar medium using new
high-resolution maps of the 8 micron, 24 micron, and 70 micron surface
brightness towards a molecular cloud in the Gum Nebula, made as part of the
Spitzer Space Telescope Galactic First Look Survey. The maps are correlated
with 100 micron images measured with IRAS. At 24 and 70 micron, the spatial
power spectrum of surface brightness follows a power law with spectral index
-3.5. At 24 micron, the power law behavior is remarkably consistent from the
0.2 degree size of our maps down to the 5 arcsecond spatial resolution. Thus,
the structure of the 24 micron emission is self-similar even at milliparsec
scales. The combined power spectrum produced from Spitzer 24 micron and IRAS 25
micron images is consistent with a change in the power law exponent from -2.6
to -3.5. The decrease may be due to the transition from a two-dimensional to
three-dimensional structure. Under this hypothesis, we estimate the thickness
of the emitting medium to be 0.3 pc.Comment: 13 Pages, 3 Figures, to be published in Astrophysical Journal
Supplement Series (Spitzer Special Issue), volume 154. Uses aastex v5.
The Infrared Spectrograph on the Spitzer Space Telescope
The Infrared Spectrograph (IRS) is one of three science instruments on the
Spitzer Space Telescope. The IRS comprises four separate spectrograph modules
covering the wavelength range from 5.3 to 38micron with spectral resolutions, R
\~90 and 600, and it was optimized to take full advantage of the very low
background in the space environment. The IRS is performing at or better than
the pre-launch predictions. An autonomous target acquisition capability enables
the IRS to locate the mid-infrared centroid of a source, providing the
information so that the spacecraft can accurately offset that centroid to a
selected slit. This feature is particularly useful when taking spectra of
sources with poorly known coordinates. An automated data reduction pipeline has
been developed at the Spitzer Science Center.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 6 pages, 4 figure
The galactic first-look survey with the Spitzer space telescope
The galactic first look survey (GFLS) of the Spitzer space telescope was executed during 1â11 December 2003 as one of the first science observations during nominal operations. The aim of the FLS is to provide a characteristic âfirst-lookâ at the mid-and far-infrared sky at sensitivities that allow the detection of point sources â100 times fainter than those in previous systematic large-area surveys. The whole program took 35.5 h to complete and consisted of the following elements:
â˘Galactic longitudinal strips of size 15Ⲡà 1° with IRAC and MIPS at l = 105.6° and 254.4° and various galactic latitudes.
â˘10Ⲡà 10ⲠIRAC maps at l = 97.5° and b = 0°, Âą4°, and +16°.
â˘Coverage of L1228 with 2° scan maps.
Even at these large distances from the galactic center, confusion sets a limit to the detection of point sources in the galactic plane for IRAC channel 1 (3.6 Îźm) at 100 ÎźJy â 16.1^m. As positive galactic latitudes were mainly sampled at l = 97.5° and 105.6° and negative latitudes at 254.4° galactic longitude, the observations are well suited to derive information on the warp of the galactic disk. In order to reproduce the source counts from the GFLS we had to assume an amplitude of the warp within 20% of that derived from 2MASS. The whole survey is included in the Spitzer science archive which opened in April 2004
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