1,575 research outputs found
NGC 1058: Gas motions in an extended, quiescent spiral disk
Researchers investigate in detail the motion of gas in the galaxy NGC 1058 using the very large array (VLA) to map the emission in the 21-cm line. This galaxy is so nearly face-on that the contribution to the line width due to the variation of the rotational velocity across the D-array beam is small compared with the random z-motion of the gas. Researchers confirm results of earlier studies (Lewis 1987, A. and A. Suppl., 63, 515; van der Kruit and Shostak 1984, A. and A., 134, 258) of the galaxy's total neutral hydrogen (HI) and kinematics, including the fact that the rotation curve drops faster than Keplerian at the outer edge of the disk, which is interpreted as a fortuitous twist of the plane of rotation in the outer disk. However, their very high velocity resolution (2.58 km s(exp -1) after Hanning smoothing) coupled with good spatial resolution, allows researchers to measure more accurately the line width, and even to some extent its shape, throughout the disk. One of the most interesting results of this study is the remarkable constancy of the line width in the outer disk. From radius 90 to 210 seconds the Gaussian velocity dispersion (sigma sub nu) of the 21-cm line has a mean value of 5.7 km s(exp -1) (after correcting for the spectral resolution) with a dispersion of less than 0.9 km s(exp -1) (after correcting for the spectral resolution) with a dispersion of less than 0.9 km s(exp -1). Translating this directly into a kinetic temperature (Doppler temperature): T sub Dopp equals 121K (sigma sub mu exp 2/(km s(exp -1) (exp 2) gives 4000 K, with a dispersion of less than 1500 K over the outer disk. This constancy is observed even when comparing the spiral arms versus inter-arm regions, which in the radius range from 100 to 150 seconds the surface density modulates (defined as the ratio N sub peak -N sub trough/N sub peak + N sub trough) from 0.5 to 0.25 in the range 150 to 200 seconds
Minimizing Strong Telluric Absorption in Near Infra-red Stellar Spectra
We have obtained high resolution spectra (R = 25000) of an A star over
varying airmass to determine the effectiveness of telluric removal in the limit
of high signal to noise. The near infra-red line HeI at 2.058 microns, which is
a sensitive indicator of physical conditions in massive stars, supergiants, HII
regions and YSOs, resides among pressure broadened telluric absorption from
carbon dioxide and water vapor that varies both in time and with observed
airmass.
Our study shows that in the limit of bright stars at high resolution,
accuracies of 5% are typical for high airmass observations (greater than 1.9),
improving to a photon-limited accuracy of 2% at smaller airmasses (less than
1.15). We find that by using the continuum between telluric absorption lines of
a ro-vibrational fan a photon-limited 1% accuracy is achievable.Comment: 14 pages, 7 figures. Accepted for publication in PAS
Interstellar gas and dust in the young cluster IC 348
We have completed a multiband absorption- and emission-line study of a star embedded in the young cluster IC 348, to determine the environmental effect of star formation on the interstellar medium (ISM) local to the region. The hottest and youngest star in IC 348 is BD+31°643, a B5 V star which samples the inner bright nebular region. The nearby star o Per, which lies only 8 to the north and is thought to lie beyond IC 348, samples the gas and dust which has not been processed by very recent star formation. We speculate that the ISM throughout the region was originally the same as that currently seen toward o Per, but now the contrasting environmental conditions due to the recent star formation have led to marked differences in the atomic, molecular, and dust characteristics of IC 348. These contrasts include what we have termed a ``composite\u27\u27 UV extinction curve for BD+31°643, evidence for enhanced density and enhanced depletions within IC 348 and very different molecular abundances in the interstellar sightline to BD+31°643. Toward BD+31°643, we find a higher column density of CH, but lower CN and very much higher CH + than measured toward o Per. We conclude that the physical and chemical state of the gas and dust has been altered by local processes and conditions within IC 348. The characteristics of the ISM in IC 348, via our study of the star BD+31°643, closely resemble those seen toward Oph, another sight line passing through a bright nebular region. However, the stars are not as hot in IC 348 as in Ophiuchus, so their effect on the local ISM is not as severe
Interstellar gas and dust in the young cluster IC 348
We have completed a multiband absorption- and emission-line study of a star embedded in the young cluster IC 348, to determine the environmental effect of star formation on the interstellar medium (ISM) local to the region. The hottest and youngest star in IC 348 is BD+31°643, a B5 V star which samples the inner bright nebular region. The nearby star o Per, which lies only 8 to the north and is thought to lie beyond IC 348, samples the gas and dust which has not been processed by very recent star formation. We speculate that the ISM throughout the region was originally the same as that currently seen toward o Per, but now the contrasting environmental conditions due to the recent star formation have led to marked differences in the atomic, molecular, and dust characteristics of IC 348. These contrasts include what we have termed a ``composite\u27\u27 UV extinction curve for BD+31°643, evidence for enhanced density and enhanced depletions within IC 348 and very different molecular abundances in the interstellar sightline to BD+31°643. Toward BD+31°643, we find a higher column density of CH, but lower CN and very much higher CH + than measured toward o Per. We conclude that the physical and chemical state of the gas and dust has been altered by local processes and conditions within IC 348. The characteristics of the ISM in IC 348, via our study of the star BD+31°643, closely resemble those seen toward Oph, another sight line passing through a bright nebular region. However, the stars are not as hot in IC 348 as in Ophiuchus, so their effect on the local ISM is not as severe
Near Infrared Spectroscopy of G29.96-0.02: The First Spectral Classification of the Ionizing Star of an Ultracompact HII Region
We have obtained the first classification spectrum and present the first
direct spectral classification of the ionizing star of an ultracompact HII
region. The ultracompact HII region is G29.96-0.02, a well-studied object with
roughly twice solar metallicity. The near infrared K-band spectrum of the
ionizing star exhibits CIV and NIII emission and HeII absorption, but lines of
HI and HeI are obliterated by nebular emission. We determine that the star has
a spectral type of O5 to O7 or possibly O8. We critically evaluate limits on
the properties of the star and find that it is compatible with zero-age
main-sequence properties only if it is binary and if a significant fraction of
the bolometric luminosity can escape from the region. G29.96-0.02 will now be
an excellent test case for nebular models, as the properties of the ionizing
star are independently constrained.Comment: To appear in ApJ Letters. 7 pages and 4 figure
The Iowa Homemaker vol.21, no.3
Freshmen – Please Note, page 2
Hospital Research, Ann Koebel, page 3
Orchids to Pat, page 4
The Army Eats Well, Mary I. Barber, page 5
Making Things Grow, Betty Ann Iverson, page 6
Look Before You Snap, Kathryn Monson, page 7
Major Departments on Review, Elizabeth Murfield, page 8
Patriotic Sally, Patricia Hayes, page 10
What’s New in Home Economics, Dorothy Olson, page 12
Summer Job Holders Reap Experience, page 14
A List of Don’ts, Costume Design Class, page 15
We Salute Campus Leaders, Margaret Kirchner, page 16
Home Economics Looks to Future, M. L. Morton, page 17
Behind Bright Jackets, Julie Wendel, page 18
Alums in the News, Mary Elizabeth Sather, page 20
Nutrition for Defense, Dorothy Ann Roost, page 22
That Personal Touch, Margaret Ann Clarke, page 23
Journalistic Spindles, Elizabeth Hanson, page 2
The Spectroscopic Orbit of the Evolved Binary HD 197770
We have used spectra taken between 1992 and 1997 to derive the spectroscopic
orbit of the eclipsing double-lined spectroscopic binary HD 197770. This binary
has a period of 99.69 +/- 0.02 days and K amplitudes of 31.2 +/- 0.8 and 47.1
+/- 0.4 km s^{-1} for components A & B, respectively. The msin^{3}i values for
A & B are 2.9 and 1.9, respectively, and are close to the actual masses due to
the eclipsing nature of this binary. Both components of HD 197770 have spectral
types near B2 III. This means both components are undermassive by about a
factor of five and, thus, evolved stars. Additional evidence of the evolved
nature of HD 197770 is found in 25, 60, and 100 micron IRAS images of HD
197770. These images show 2 apparent shells centered on HD 197770; a bright 60
micron shell with a 14' diameter and a larger (1.2 degeree diameter)
bubble-like feature. At least one of the components of HD 197770 is likely to
be a post-AGB star.Comment: will be published in the AJ (1998 June), also availible at
http://snake.phys.lsu.edu/~gordon/papers/hd197770.htm
Resource Planning for Neglected Tropical Disease (NTD) Control Programs: Feasibility Study of the Tool for Integrated Planning and Costing (TIPAC).
<p>Resource Planning for Neglected Tropical Disease (NTD) Control Programs: Feasibility Study of the Tool for Integrated Planning and Costing (TIPAC)</p
Target Selection for SETI: 1. A Catalog of Nearby Habitable Stellar Systems
In preparation for the advent of the Allen Telescope Array, the SETI
Institute has the need to greatly expand its former list of ~2000 targets
compiled for Project Phoenix, a search for extraterrestrial technological
signals. In this paper we present a catalog of stellar systems that are
potentially habitable to complex life forms (including intelligent life), which
comprises the largest portion of the new SETI target list. The Catalog of
Nearby Habitable Systems (HabCat) was created from the Hipparcos Catalogue by
examining the information on distances, stellar variability, multiplicity,
kinematics and spectral classification for the 118,218 stars contained therein.
We also make use of information from several other catalogs containing data for
Hipparcos stars on X-ray luminosity, CaII H&K activity, rotation, spectral
types, kinematics, metallicity, and Stroemgren photometry. Combined with
theoretical studies on habitable zones, evolutionary tracks and third body
orbital stability, these data were used to remove unsuitable stars from HabCat,
leaving a residue of stars that, to the best of our current knowledge, are
potentially habitable hosts for complex life. While this Catalog will no doubt
need to be modified as we learn more about individual objects, the present
analysis results in 17,129 Hipparcos "habstars" near the Sun (75% within 140
pc), ~2200 of which are known or suspected to be members of binary or triple
star systems.Comment: 42 pages, 14 figures, accepted by ApJ Supp, to appear in v145, March
200
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