-
C. A. Grady,
K Hamaguchi,
G Schneider,
B. Stecklum, B. E. Woodgate,
J. E. McCleary,
G. M. Williger,
M. L. Sitko,
F. Ménard,
Th. Henning, [......],
D. Wilner,
M. Silverstone,
J. -C. Bouret,
H. Meusinger,
M. Clampin,
S Kim,
R. Petre,
M. Sahu,
M. Endres,
K. A. Collins
[show abstract]
[hide abstract]
ABSTRACT: Accretion is a fundamental process which establishes the dynamics of the protoplanetary disk and the final properties of the forming star. In solar-type stars, the star-disk coupling is determined by the magnetic field structure, which is responsible for funneling material from the disk midplane to higher latitudes on the star. Here, we use pan-chromatic data for the Herbig Ae star MWC 480 to address whether similar processes occur in intermediate-mass stars. MWC 480 has X-ray emission typical of actively accreting Herbig Ae stars, but with ~10Ãâ more photoelectric absorption than expected from optical and FUV data. We consider three sources for the absorption: the disk, absorption in a wind or jet, and accretion. While we detect the disk in scattered light in a re-analysis of archival Hubble Space Telescope data, the data are consistent with grazing illumination of the dust disk. We find that MWC 480's disk is stratified, geometrically thin, and is not responsible for the observed photoelectric absorption. MWC 480 drives a bipolar jet, but with a mass-loss rate that is low compared to other Herbig Ae stars, where the outflow is more favorably oriented and enhanced photoelectric absorption is not seen. This excludes a jet or wind origin for the enhanced photoelectric absorption. We compare MWC 480's O VI emission with other Herbig Ae stars. The distribution of the emission in inclination, and lack of a correlation of profile shape and system inclination excludes equatorially confined accretion for the FUSE Herbig Ae stars. The photoelectric absorption data further suggest that the accretion footprint on MWC 480 and other Herbig Ae stars is located at high-temperate, rather than polar, latitudes. These findings support the presence of funneled accretion in MWC 480 and Herbig Ae stars, strengthening the parallel to T Tauri stars.
The Astrophysical Journal 08/2010; · 6.02 Impact Factor
-
R. A. Kimble, B. E. Woodgate,
C. W. Bowers,
S. B. Kraemer,
M. E. Kaiser,
T. R. Gull,
S. R. Heap,
A. C. Danks,
A. Boggess,
R. F. Green, [......],
R. J. Hill,
W. B. Landsman,
E. M. Malumuth,
C. Standley,
M. Blouke,
A. Grusczak,
R. Reed,
R. D. Robinson,
J. A. Valenti,
and T. Wolfe
[show abstract]
[hide abstract]
ABSTRACT: The Space Telescope Imaging Spectrograph (STIS) was successfully installed into the Hubble Space Telescope (HST) in 1997 February, during the second HST servicing mission, STS-82. STIS is a versatile spectrograph, covering the 115-1000 nm wavelength range in a variety of spectroscopic and imaging modes that take advantage of the angular resolution, unobstructed wavelength coverage, and dark sky offered by the HST. In the months since launch, a number of performance tests and calibrations have been carried out and are continuing. These tests demonstrate that the instrument is performing very well. We present here a synopsis of the results to date.
The Astrophysical Journal 01/2009; 492(2):L83. · 6.02 Impact Factor
-
A. B. Schultz,
F. Allard,
M. Clampin,
M. McGrath,
F. C. Bruhweiler,
J. A. Valenti,
P. Plait,
S. Hulbert,
S. Baum, B. E. Woodgate,
C. W. Bowers,
R. A. Kimble,
S. P. Maran,
H. W. Moos,
and F. Roesler
[show abstract]
[hide abstract]
ABSTRACT: We report the first Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) CCD spectroscopy of the bona fide brown dwarf Gliese 229B. The optical spectrum shows absorptions of Cs I at 8944 Å and water vapor bands at 9300-9600 Å. Strong CaH, FeH, TiO, and VO bands observed in late M dwarfs are absent from the spectrum of Gliese 229B. The formation of dust grains may explain the absence of strong atomic lines and molecular bands of these refractory elements. The broad spectral coverage obtained helps resolve current speculations about the presence of dust clouds in the atmosphere of cool brown dwarfs. We find the slope of the STIS/CCD spectrum and the lack of flux detected shortward of 8000 Å strongly supports the presence of dust hazes suspended in the photosphere of Gl 229B rather than a complete settling of the grains to regions below the photosphere.
The Astrophysical Journal 01/2009; 492(2):L181. · 6.02 Impact Factor
-
C. A. Grady,
G. Schneider,
K. Hamaguchi,
M. L. Sitko,
W. J. Carpenter,
D. Hines,
K. A. Collins,
G. M. Williger, B. E. Woodgate,
Th. Henning,
F. Ménard,
D. Wilner,
R. Petre,
P. Palunas,
A. Quirrenbach,
J. A. Nuth III,
M. D. Silverstone,
and J. S. Kim
[show abstract]
[hide abstract]
ABSTRACT: We trace the disk of HD 169142 (A8 Ve) from 0.57'' to 1.4'' (≈80-200 AU projected distance) in 1.1 μm scattered light with HST NICMOS coronagraphy. The azimuthally symmetric disk has a peak azimuthally medianed surface brightness (SB) of ≈5 mJy arcsec-2 at 0.57'' from the star, and drops r-3. This radial SB profile is consistent with the presence of spatially resolved PAH emission and a Meeus group I IR SED only if the inner disk is either substantially flatter than the outer disk or partially devoid of material. Analysis of new HST ACS FUV imagery in tandem with archival IUE data indicates acc ≤ 10-9 M☉ yr-1. We estimate the age of HD 169142 to be 6 Myr by identifying 2MASS 18242929-2946559, located 9.3'' to the southwest, as a 130 mas separation weak-line T Tauri binary that is comoving with HD 169142 at the 4 σ confidence level. We find no evidence for any additional stellar companion in either the ACS or Chandra ACIS-S data at r ≤ 1''. HD 169142 has previously been interpreted as a slowly rotating, chemically peculiar star. However, by combining the disk inclination and v sin i from the literature, we find that the star has vequatorial ≈ 240 km s-1, making it a rapid rotator, similar to Altair or Vega. The UV data for HD 169142 are consistent with gravity darkening, while the X-ray luminosity and spectrum resembles early F stars at the age of the β Pictoris moving group, rather than mid-A stars. In this context, spectral features previously interpreted as evidence for chemical peculiarity are more likely to reflect the presence of a strong photospheric latitudinal temperature gradient. With such a gradient, HD 169142 should closely resemble Vega at the epoch of central disk clearing.
The Astrophysical Journal 12/2008; 665(2):1391. · 6.02 Impact Factor
-
C. A. Grady, B. E. Woodgate,
C. W. Bowers,
T. R. Gull,
M. L. Sitko,
W. J. Carpenter,
D. K. Lynch,
R. W. Russell,
R. B. Perry,
G. M. Williger,
A. Roberge,
Jean-Claude Bouret,
and Meena Sahu
[show abstract]
[hide abstract]
ABSTRACT: STIS white-light coronagraphic imaging has been carried out for 14 nearby, lightly reddened Herbig Ae stars, providing data on the environments and disks associated with these stars. No disks are detected in our data when the Herbig Ae star is accompanied by a stellar companion at r ≤ 2''. We find that the optical visibility of protoplanetary disks associated with Herbig Ae stars at r ≥ 50-70 AU from the star is correlated with the strength of the mid-IR PAH features, particularly 6.2 μm. These features, like the FUV fluorescent H2 emission, trace the presence of material sufficiently far above the disk midplane that it is directly illuminated by the star's FUV radiation. In contrast, measures of the bulk properties of the disk, including ongoing accretion activity, mass, and the submillimeter slope of the SED, do not correlate with the surface brightness of the optical nebulosity. Modelers have interpreted the appearance of the IR SED and the presence of emission from warm silicate grains at 10 μm as a measure of geometrical shadowing by material in the disk near the dust sublimation radius of 0.5 AU. Geometrical shadowing sufficient to render a disk dark to distances as large as 500 AU from a star would require that the star be optically visible only if viewed essentially pole-on, in disagreement with our program star system inclinations. Rather than invoking shadowing to account for the optically dark disks, the correlation of the STIS detections with PAH emission features suggests a correlation with disk flaring and an anticorrelation with the degree of dust settling toward the midplane. If this correlation continues to lower levels, the STIS data suggest that improvements in coronagraph performance that suppress the residual scattered and diffracted stellar light by an additional factor of ≥10 should render the majority of disks associated with nearby Herbig Ae stars detectable.
The Astrophysical Journal 12/2008; 630(2):958. · 6.02 Impact Factor
-
C. A. Grady,
E. F. Polomski,
Th. Henning,
B. Stecklum, B. E. Woodgate,
C. M. Telesco,
R. K. Piña,
T. R. Gull,
A. Boggess,
C. W. Bowers, [......],
R. A. Kimble,
S. Kraemer,
D. Lindler,
J. L. Linsky,
S. P. Maran,
H. W. Moos,
P. Plait,
F. Roesler,
J. G. Timothy,
and D. Weistrop
[show abstract]
[hide abstract]
ABSTRACT: Coronagraphic imaging of the nearest Herbig Be star with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope, Ks (2.15 μm) imaging with ADONIS at the 3.6 m telescope at La Silla, and mid-infrared imaging with OSCIR using the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory confirm the detection of the disk reported by Pantin et al. and map the disk out to 5'' (~515 AU) in the optical and at Ks. While the source is unresolved at 10 and 18 μm, it can be traced to 15 at 11.7 μm. We confirm the change in the radial dependence of the disk surface brightness near 27 seen at 1.6 μm by Augereau et al. at Ks. No such break in the power law is seen in the optical. The STIS data reveal spiral dark lane structure, making HD 100546 the third near–zero-age main-sequence Herbig Ae/Be star with structure more than 100 AU from the star. We also optically detect a low surface brightness envelope extending 10'' (1000 AU) from the star, in addition to nebulosity, which is probably associated with DC 292.6-7.9. The survival of the envelope through essentially the entire pre–main-sequence lifetime of the star, coupled with the absence of physical companions within 1500 AU of the star, suggests that envelope lifetimes owe more to the star-forming environment than to mass-loss activity from the Herbig Ae/Be star.
The Astronomical Journal 12/2007; 122(6):3396. · 4.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present Spitzer Space Telescope observations of the z=2.38 Lyα-emitter over-densityassociated with galaxy cluster J2143-4423, the largest
known structure (110 Mpc)above z=2.We imaged 22 of the 37 known Lyα-emitters within the filament-like structure,using the
MIPS 24μm band. We detected 6 of the Lyα-emitters, including 3 of the 4 clouds of extended (>50kpc) Lyα emission, also known
as Lyα Blobs.Conversion from rest-wavelength 7μm to total far-infrared luminosityusing locally derived correlations suggests
all the detected sources are in the class of ULIRGs, with some reaching Hyper-LIRG energies. Lyα blobs frequently show evidence
for interaction, either in HST imaging,or the proximity of multiple MIPS sources within the Lyα cloud. This connection suggests that interaction or even
mergers may be related to the production of Lyα blobs. A connection to mergersdoes not in itself help explain the origin of
the Lyα blobs, as most of the suggested mechanisms for creating Lyα blobs (starbursts, AGN, cooling flows) could alsobe associated
with galaxy interactions.
10/2007: pages 358-362;
-
Mary Elizabeth Kaiser,
J. W. Kruk,
S. R. McCandliss,
D. J. Sahnow,
W. Dixon,
P. D. Feldman,
H. Moos,
A. Riess,
B. J. Rauscher,
R. A. Kimble,
J. P. Gardner, B. E. Woodgate,
R. C. Bohlin,
S. E. Deustua,
R. Kurucz,
S. Perlmutter,
E. L. Wright
[show abstract]
[hide abstract]
ABSTRACT: ACCESS is a proposed series of rocket-borne sub-orbital missions whose
purpose is to establish a network of standard stars with absolute fluxes
that are directly traceable to ground based laboratory calibration
standards maintained by NIST. Our goal is to obtain an absolute
spectrophotometric calibration accuracy of <1% in the 0.35-1.7 micron
bandpass at a spectral resolution of greater than 500. This represents a
significant improvement in the absolute calibration in the NIR bandpass.
This fundamental astrophysics experiment will establish the first links
in a chain of stellar calibrators including standard stars (10th
magnitude) observable by major telescopes, thus enabling the ultimate
calibration to extend to faint magnitudes. This calibration program is
important for a broad range of missions and relevant to many
astrophysical problems. It is fundamental to photometrically based dark
energy missions which use supernova type Ia and will provide the first
steps in the calibration path required to support the determination of
brightness as a function of distance for SNIae. In addition, it will
enable improved stellar atmosphere models, furthering our understanding
of stellar physics.
04/2007; 39:274.
-
[show abstract]
[hide abstract]
ABSTRACT: We review the contribution of FUV spectroscopy in furthering our
understanding of planetary system evolution over the first 20-30 Myr. In
tandem with high spatial resolution imagery of circumstellar disks,
secure dating of young stars, and IR and x-ray data, FUSE has
established that the disks around stars with 0.7≤M≤2.5
Msun evolve on similar timescales and in the same way.
FUSE has unequivocably demonstrated that Herbig Ae stars closely
resemble T Tauri stars while actively accreting. Absorption-line studies
of ZAMS A stars have revealed the presence of planetesimals in the
disks, including icy bodies up to 20 AU from the star. Most importantly,
FUSE constrains the epoch of gaseous giant planet formation to be ≤12
Myr both for A stars and for M stars. With the recognition, and dating
of additional debris disks in our immediate vicinity, FUSE is poised to
extend these studies to additional intermediate-mass stars and to
nearby, post-T Tauri stars.
05/2006; 348:281.
-
[show abstract]
[hide abstract]
ABSTRACT: AB Aur has an FUV spectral similarity to three known Herbig Ae jet
systems whose FUSE and other FUV spectral data all have distinctive
emission profiles, and emissions in Si III]1892 and O III]1665. AB Aur
has a face-on disk and any outflow should have low proper motion, and be
largely directed in our line of sight. We report the discovery of 3
clusters of Herbig-Haro knots at projected distances near SU Aur. HST
archival imagery from 1998-2001 indicates no significant proper motion.
We present the radial velocity of the outflow, derived from Goddard
Fabry-Perot at the Apache Point Observatory's 3.5m telescope, and
supporting long slit spectroscopy with Dual Imaging Spectrograph. The
inclination of HH flow, its relation to AB Aur, and the epoch of the
knot ejections with implications for FU Orionis activity in this Herbig
Ae star are discussed.
Support for this study was provided under NASA RTOP 51-188-01-22.
11/2005; 37:1287.
-
[show abstract]
[hide abstract]
ABSTRACT: We have carried out a deep narrow-band imaging survey of six fields with heavy-element quasar absorption lines, using the Goddard Fabry-Perot (FP) system at the Apache Point Observatory (APO) 3.5-meter telescope. The aim of these observations was to search for redshifted Ly-$\alpha$ emission from the galaxies underlying the absorbers at $z = 2.3-2.5$ and their companion galaxies. The 3 $\sigma$ sensitivity levels ranged between $1.9 \times 10^{-17}$ and $5.4 \times 10^{-17}$ erg s$^{-1}$ cm$^{-2}$ in observed-frame Ly-$\alpha$ flux. No significant Ly-$\alpha$ emitters were detected at $> 3 \sigma$ level. The absence of significant Ly-$\alpha$ emission implies limits on the star formation rate (SFR) of 0.9-2.7 $M_{\odot}$ yr$^{-1}$ per 2-pixel x 2-pixel region, if no dust attenuation is assumed. We compare our results with those from other emission-line studies of absorber fields and with predictions for global average SFR based on the models of cosmic chemical evolution. Our limits are among the tightest existing constraints on Ly-$\alpha$ emission from galaxies in absorber fields, but are consistent with many other studies. In the absence of dust attenuation, these studies suggest that SFRs in a large fraction of objects in the absorber fields may lie below the global mean SFR. However, it is possible that dust attenuation is responsible for the low emission line fluxes in some objects. It is also possible that the star-forming regions are compact and at smaller angular separations from the quasar than the width of our point spread function and, get lost in the quasar emission. We outline future observations that could help to distinguish between the various possibilities.
10/2005;
-
[show abstract]
[hide abstract]
ABSTRACT: Far Ultraviolet Spectroscopic Explorer (FUSE) far-UV (FUV) spectra
provide an unique view of accretion and stellar activity in nearby,
minimally reddened pre-main sequence stars. We present first results of
the FUSE Legacy study of young, intermediate-mass stars. The FUSE data
show that over 1--10 Myr, Herbig Ae stars closely resemble classical T
Tauri stars by having FUV excess light and a rich emission-line
spectrum. The line profile shapes are distinctive and include
double-peaked C III 1176 A profiles. The blue emission component in C
III 1176 is at the jet footprint velocity in the two FUSE Herbig Ae
stars with known microjets. These stars also have O III] and Si III]
emission in Space Telescope Imaging Spectrograph and archival
International Ultraviolet Explorer data. We report the presence of
similar emission profiles in MWC 480 and AB Aur, suggesting that these
stars are both driving microjets. The majority of the Herbig Ae stars
with FUSE data have O VI surface fluxes in a narrow range.
Non-accreting, co-eval A stars, mostly with known debris disks, have O
VI surface fluxes a factor of 50--100 below the level seen in the
accreting systems. The FUSE data permit us to identify several
transitional systems with low or no detectable FUV excesses, and with
infrared spectral energy distributions suggesting central clearing with
cavities as large as r=10 AU, which may be due to dynamical clearing by
planets. The scarcity of stars with activity levels intermediate between
the Herbig Ae stars and the debris disks suggests that activity drops
rapidly with the end of accretion, in contrast to solar-type stars, but
persists to at least the age of Beta Pictoris at 12 Myr. This study uses
data obtained under FUSE programs C126, D065, and E510, as well as
archival FUSE data and HST data from HST-GTO-8801 and 8065.
11/2004; 36:1364.
-
C. A. Grady,
C. R. Proffitt,
E. Malumuth, B. E. Woodgate,
T. R. Gull,
C. W. Bowers,
S. R. Heap,
R. A. Kimble,
D. Lindler,
P. Plait,
A. Weinberger
[show abstract]
[hide abstract]
ABSTRACT: The unfiltered Space Telescope Imaging Spectrograph (STIS) CCD in tandem
with focal plane wedges and a Lyot stop provides a simple white-light
coronagraph with a bandpass of 0.2-1.0 μm, which has been used since
late 1998 to image nebulosity around stars in the ranges
0.34<=V<=14 and -0.03<=B-V<=1.65. The residual starlight
seen in STIS coronagraphic images includes diffraction spikes due to the
Hubble Space Telescope (HST) secondary support structure, lacks distinct
Airy rings, and varies smoothly with radius from the star. The
point-spread function (PSF) shape is a strong function of the source
spectral energy distribution: we find that the PSF template needs to
differ from the occulted source color by Δ(B-V)<=0.08 mag.
Optimal PSF removal is achieved for contemporary template observations
matched to HST orbital phase of the science observations. Use of
noncontemporary PSF templates can degrade the limiting contrast by up to
a factor of 10-12 at r<=2''. These systematic effects are
negligible when the nebular surface brightness is comparable to the
residual starlight, and they become progressively more important as
surface brightness decreases. STIS has been used to detect circumstellar
envelopes and protoplanetary disks with surface brightnesses spanning
10-4 to 10-7 per HST resolution element per
Fstar at 2" from the star, debris disks with
FIR/Fstar>=0.001, and emission-line nebulosity
associated with bipolar outflows. The limiting contrast for single-orbit
integrations with the star placed at a location where the coronagraphic
wedge is 1.0" wide is 10-8 per HST resolution element per
Fstar for 6<=V<=8 stars. Deeper imagery can be obtained
by placing the star off the active detector area. When the star is 5"
from the detector, a limiting contrast for a single-orbit integration of
2.5×10-10 per HST resolution element per
Fstar is reached. At this contrast level, background objects
and the stellar color variability prevent further improvement by
co-adding data from multiple orbits.
Based on observations made with the NASA/ESA Hubble Space Telescope,
obtained at the Space Telescope Science Institute, which is operated by
the Association of Universities for Research in Astronomy, Inc., under
NASA contract NAS 5-26555. This study is part of the STIS IDT
protoplanetary disk key project.
Publications of the Astronomical Society of the Pacific 08/2003; 115:1036-1049. · 3.58 Impact Factor
-
T. M. Tripp,
E. B. Jenkins,
G. M. Williger,
S. R. Heap,
C. W. Bowers,
A. C. Danks,
R. Dave,
R. F. Green,
T. R. Gull,
C. L. Joseph,
M. E. Kaiser,
D. Lindler,
R. J. Weymann, B. E. Woodgate
[show abstract]
[hide abstract]
ABSTRACT: Using high S/N STIS echelle spectra (FWHM=7 km/s) of 3C 273, we constrain the metallicities of two Lya clouds in the vicinity of the Virgo cluster. We detect C II, Si II, and Si III absorption lines in the Lya absorber at z = 0.00530. Previous observations with FUSE have revealed Ly beta - Ly theta lines at this redshift, thereby accurately constraining N(H I). We model the ionization of the gas and derive [C/H] = -1.2^{+0.3}_{-0.2}, [Si/C] = 0.2+/-0.1, and log n_{H} = -2.8+/-0.3. The model implies a small absorber thickness, ~70 pc, and thermal pressure p/k ~ 40 cm^{-3} K. It is most likely that the absorber is pressure confined by an external medium because gravitational confinement would require a very high ratio of dark matter to baryonic matter. Based on Milky Way sight lines in which carbon and silicon abundances have been reliably measured in the same interstellar cloud (including new measurements presented herein), we argue that the overabundance of Si relative to C is not due to dust depletion. Instead, this probably indicates that the gas has been predominately enriched by Type II supernovae. Such enrichment is most plausibly provided by an unbound galactic wind, given the absence of galaxies within a projected distance of 100 kpc and the presence of galaxies capable of driving a wind at larger distances. We also constrain the metallicity and physical conditions of the Virgo absorber at z = 0.00337 based on detections of O VI and H I and an upper limit on C IV. If this absorber is collisionally ionized, the O VI/C IV limit requires T > 10^{5.3} K. For either collisional ionization or photoionization, we find that [O/H] > -2.0 at z = 0.00337.
05/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: Revealing faint circumstellar nebulosity and faint stellar or substellar companions to bright stars typically requires use of techniques for rejecting the direct, scattered, and diffracted light of the star. One such technique is Lyot coronagraphy. We summarize the performance of the white-light coronagraphic capability of the Space Telescope Imaging spectrograph, on board the Hubble Space Telescope.
02/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: We have developed a model that allows us to defringe slitless 2-dimensional spectra taken with the Space Telescope Imaging Spectrograph (STIS). An IDL tool has been developed which allows the user to defringe any spectrum obtained with the G750L grating on STIS. This technique has been employed to model the fringing on Wide Field Camera 3 (WFC3) flight candidate CCDs.
02/2002;
-
H. W. Moos,
K. R. Sembach,
A. Vidal-Madjar,
D. G. York,
S. D. Friedman,
G. Hebrard,
J. W. Kruk,
N. Lehner,
M. Lemoine,
G. Sonneborn, [......],
C. Oliveira,
K. Roth,
D. J. Sahnow,
B. D. Savage,
J. M. Shull,
T. M. Tripp,
E. J. Weiler,
B. Y. Welsh,
E. Wilkinson, B. E. Woodgate
[show abstract]
[hide abstract]
ABSTRACT: Observations obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) have been used to determine the column densities of D I, O I, and N I along seven sight lines that probe the local interstellar medium (LISM) at distances from 37 pc to 179 pc. Five of the sight lines are within the Local Bubble and two penetrate the surrounding H I wall. Reliable values of N(H I) were determined for five of the sight lines from HST data, IUE data, and published EUVE measurements. The weighted mean of D I/H I for these five sight lines is (1.52 +/- 0.08) x10-5 (1 sigma uncertainty in the mean). It is likely that the D I/H I ratio in the Local Bubble has a single value. The D I/O I ratio for the five sight lines within the Local Bubble is (3.76 +/- 0.20) x10-2. It is likely that the O I column densities can serve as a proxy for H I in the Local Bubble. The weighted mean for O I/H I for the seven FUSE sight lines is (3.03 +/-0.21) x10-4, comparable to the weighted mean (3.43 +/- 0.15) x10-4 reported for 13 sight lines probing larger distances and higher column densities (Meyer et al. 1998, Meyer 2001). The FUSE weighted mean of N I/H I for the five sight lines is half that reported by Meyer et al. (1997) for seven sight lines with larger distances and higher column densities. This result combined with the variability of O I/N I (six sight lines) indicates that at the low column densities found in the LISM, nitrogen ionization balance is important. Thus, unlike O I, N I cannot be used as a proxy for H I or as a metallicity indicator in the LISM. Subject Headings: cosmology: observations- ISM: abundances- ISM: evolution - Galaxy:abundances-Ultraviolet:ISM
01/2002;
-
[show abstract]
[hide abstract]
ABSTRACT: Far-ultraviolet spectra were obtained of the active cool star AB Doradus (HD 36705) during the calibration and checkout period of the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. Observations in this early phase of the mission were taken at a resolving power of 12,000--15,000 (#20--25 km s #1 ) and covered the spectral range 905--1187 A . The integrated spectrum exhibits strong, rotationally broadened stellar emission from C iii (ll977, 1175) and O vi (ll1032, 1037) and many weaker lines. Strong emission lines of C iii and O vi exhibit broad wings. The C iii l977 profile shows blueshifted absorption at #30 km s #1 , and C ii l1036 absorption appears superposed on emission in the wing of O vi l1037. Rotational modulation of C iii and O vi is present, in harmony with its photometric variability. Flares were detected in the brightest lines, and subexposures were analyzed to examine flux and profile variations. Downflows that extend to 600 km s #1 during a flare are found in the O vi profiles. These early observations demonstrate that FUSE will be an exceptional instrument for studying chromospheres in cool stars. Subject headings: stars: chromospheres --- stars: flare --- stars: individual (AB Doradus) --- stars: pre--main-sequence --- ultraviolet: stars 1. OBSERVATIONS AND DATA ANALYSIS AB Doradus is a nearby (15 pc), rapidly rotating (P= rot hr, km s #1 ), K0--2 IV--V pre--main-sequence 12.4 v sin i=90 star that exhibits high activity and frequent flaring (e.g., Collier Cameron et al. 1999; Schmitt, Cutispoto, & Krautter 1998; Vilhu et al. 1998). It is the first cool star observed by the Far Ultraviolet Spectroscopic Explorer (FUSE; see Moos et al. 2000). Observations were obtained on 1999 October 20 and 22, in the LiF channels (ll987--1187), a...
05/2001;
-
P. J. Francis,
G. M. Williger,
N. R. Collins,
P. Palunas,
E. M. Malumuth, B. E. Woodgate,
H. I. Teplitz,
A. Smette,
R. S. Sutherland,
A. C. Danks,
R. S. Hill,
D. Lindler,
R. A. Kimble,
S. A. Heap,
J. B. Hutchings
[show abstract]
[hide abstract]
ABSTRACT: We present Hubble Space Telescope (HST) and ground-based observations of a pair of galaxies at redshift 2.38, which are collectively known as 2142-4420 B1 (Francis et al. 1996). The two galaxies are both luminous extremely red objects (EROs), separated by 0.8 arcsec. They are embedded within a 100 kpc scale diffuse Ly-alpha nebula (or blob) of luminosity ~10^44 erg/s. The radial profiles and colors of both red objects are most naturally explained if they are young elliptical galaxies: the most distant yet found. It is not, however, possible to rule out a model in which they are abnormally compact, extremely dusty starbursting disk galaxies. If they are elliptical galaxies, their stellar populations have inferred masses of ~10^11 solar masses and ages of ~7x10^8 years. Both galaxies have color gradients: their centers are significantly bluer than their outer regions. The surface brightness of both galaxies is roughly an order of magnitude greater than would be predicted by the Kormendy relation. A chain of diffuse star formation extending 1 arcsec from the galaxies may be evidence that they are interacting or merging. The Ly-alpha nebula surrounding the galaxies shows apparent velocity substructure of amplitude ~ 700 km/s. We propose that the Ly-alpha emission from this nebula may be produced by fast shocks, powered either by a galactic superwind or by the release of gravitational potential energy. Comment: 33 pages, 9 figures, ApJ in press (to appear in Jun 10 issue)
02/2001;
-
[show abstract]
[hide abstract]
ABSTRACT: Far ultraviolet spectra were obtained of the active cool star AB Doradus (HD 36705) during the calibration and checkout period of the FUSE satellite. Observations in this early phase of the mission were taken at a resolving power of 12000-15000 (~20-25 km/s) and covered the spectral range 905-1187 A. The integrated spectrum exhibits strong, rotationally broadened stellar emission from C III (977, 1175) and O VI (1032, 1037), and many weaker lines. Strong emission lines of C III and O VI exhibit broad wings. The C III 977 profile shows blue-shifted absorption at ~30 km/s and C II 1036 absorption appears superposed on emission in the wing of O VI 1037. Rotational modulation of C III and O VI is present, in harmony with its photometric variability. Flares were detected in the brightest lines and subexposures were analyzed to examine flux and profile variations. Downflows that extend to 600 km/s during a flare are found in the O VI profiles. These early observations demonstrate that FUSE will be an exceptional instrument for studying chromospheres in cool stars.
07/2000;
