108 research outputs found
A Search for the Damped Ly-alpha Absorber at z=1.86 toward QSO 1244+3443 with NICMOS
We have carried out a high-resolution imaging search for the galaxy
associated with the damped Lyman-alpha (DLA) absorber at z=1.859 toward the
z_{em}=2.48 quasar QSO 1244+3443, using the HST and the NICMOS. Images were
obtained in the broad filter F160W and the narrow filter F187N with camera 2 on
NICMOS with the goal of detecting the rest-frame optical continuum and the
H-alpha line emission from the DLA. After PSF subtraction, two weak features
are seen at projected separations of 0.16-0.24" from the quasar. Parts of these
features may be associated with the DLA absorber, although we cannot completely
rule out that they could be artifacts of the point spread function (PSF). If
associated with the DLA, the objects would be ~1-2 h_{70}^{-1} kpc in size with
integrated flux densities of 2.5 and 3.3 mu Jy in the F160W filter, implying
luminosities at lambda_{central}=5600 A in the DLA rest frame of 4.4-5.9 x
10^{9} h_{70}^{-2} L_{solar} at z=1.86, for q0=0.5. However, no significant
H-alpha line emission is seen from these objects, suggesting low star formation
rates (SFRs). Our 3 sigma upper limit on the SFR in the DLA is 1.3 h_{70}^{-2}
M_{solar}/yr for q0 = 0.5 (2.4 h_{70}^{-2} M_{solar} yr^{-1} for q0 = 0.1).
This together with our earlier result for LBQS 1210+1731 mark a significant
improvement over previous constraints on the star formation rates of DLAs. A
combination of low SFR and some dust extinction is likely to be responsible for
the lack of H-alpha emission. Alternatively, the objects, may be associated
with the quasar host galaxy. In any case, our observations suggest that the DLA
is not a large bright proto-disk, but a compact object or a low-surface
brightness galaxy. If the two features are PSF artifacts then the constraints
on DLA properties are even more severe.Comment: 28 pages, 9 figures. Accepted for publication in The Astrophysical
Journal. Figures are given at a slightly lower resolution here, to decrease
file sizes. The higher resolution versions can be found in the Ap
NICMOS Imaging of the HR 4796A Circumstellar Disk
We report the first near infrared (NIR) imaging of a circumstellar annular
disk around the young (~8 Myr), Vega-like star, HR 4796A. NICMOS coronagraph
observations at 1.1 and 1.6 microns reveal a ring-like symmetrical structure
peaking in reflected intensity 1.05 arcsec +/- 0.02 arcsec (~ 70 AU) from the
central A0V star. The ring geometry, with an inclination of 73.1 deg +/- 1.2
deg and a major axis PA of 26.8 deg +/- 0.6 deg, is in good agreement with
recent 12.5 and 20.8 micron observations of a truncated disk (Koerner, et al.
1998). The ring is resolved with a characteristic width of less than 0.26
arcsec (17 AU) and appears abruptly truncated at both the inner and outer
edges. The region of the disk-plane inward of ~60 AU appears to be relatively
free of scattering material. The integrated flux density of the part of the
disk that is visible (greater than 0.65 arcsec from the star) is found to be
7.5 +/- 0.5 mJy and 7.4 +/- 1.2 mJy at 1.1 and 1.6 microns, respectively.
Correcting for the unseen area of the ring yields total flux densities of 12.8
+/- 1.0 mJy and 12.5 +/- 2.0 mJy, respectively (Vega magnitudes = 12.92 /+-
0.08 and 12.35 +/-0.18). The NIR luminosity ratio is evaluated from these
results and ground-based photometry of the star. At these wavelengths
Ldisk(lambda)/L*(lambda) = 1.4 +/- 0.2E-3 and 2.4 +/- 0.5E-3, giving reasonable
agreement between the stellar flux scattered in the NIR and that which is
absorbed in the visible and re-radiated in the thermal infrared. The somewhat
red reflectance of the disk at these wavelengths implies mean particle sizes in
excess of several microns, larger than typical interstellar grains. The
confinement of material to a relatively narrow annular zone implies dynamical
constraints on the disk particles by one or more as yet unseen bodies.Comment: 14 pages, 1 figure for associated gif file see:
http://nicmosis.as.arizona.edu:8000/AAS99/FIGURE1_HR4796A_ApJL.gif . Accepted
13 January 1999, Astrophyical Journal Letter
Near-Infrared Camera and Multi-Object Spectrometer Observations of the Hubble Deep Field: Observations, Data Reduction, and Galaxy Photometry
This paper presents data obtained during the NICMOS Guaranteed Time Observations of a portion of the Hubble Deep Field. The data are in a catalog format similar to the publication of the original WFPC2 Hubble Deep Field program (Williams et al.). The catalog contains 342 objects in a 49farcs1 × 48farcs4 subfield of the total observed field, 235 of which are considered coincident with objects in the WFPC2 catalog. The 3 σ signal-to-noise ratio level is at an aperture AB magnitude of approximately 28.8 at 1.6 μm. The catalog sources, listed in order of right ascension, are selected to satisfy a limiting signal-to-noise ratio criterion of greater than or equal to 2.5. This introduces a few false detections into the catalog, and users should take careful note of the completeness and reliability levels for the catalog discussed in §§ 9 and 10. The catalog also contains a test parameter indicating the results of half-catalog tests and the degree of coincidence with the original WFPC2 catalog
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High-resolution Near-Infrared Images and Models of the Circumstellar Disk in HH 30
We present Hubble Space Telescope (HST) Near-Infrared Camera and Multi-object
Spectrometer (NICMOS) observations of the reflection nebulosity associated with
the T Tauri star HH 30. The images show the scattered light pattern
characteristic of a highly inclined, optically thick disk with a prominent
dustlane whose width decreases with increasing wavelength. The reflected
nebulosity exhibits a lateral asymmetry in the upper lobe on the opposite side
to that reported in previously published Wide Field Planetary Camera 2 (WFPC2)
images. The radiation transfer model which most closely reproduces the data has
a flared accretion disk with dust grains larger than standard interstellar
medium grains by a factor of approximately 2.1. A single hotspot on the stellar
surface provides the necessary asymmetry to fit the images and is consistent
with previous modeling of the light curve and images. Photometric analysis
results in an estimated extinction of Av>~80; however, since the photometry
measures only scattered light rather than direct stellar flux, this a lower
limit. The radiative transfer models require an extinction of Av = 7,900.Comment: Accepted for publication in Ap.
NICMOS Imaging of a Damped Lyman-alpha Absorber at z=1.89 toward LBQS 1210+1731 : Constraints on Size and Star Formation Rate
We report results of a high-resolution imaging search (in rest frame
H- and optical continuum) for the galaxy associated with the damped
Lyman- (DLA) absorber at toward the quasar
LBQS 1210+1731, using HST/NICMOS. After PSF subtraction, a feature is seen in
both the broad-band and narrow-band images, at a projected separation of
0.25\arcsec from the quasar. If associated with the DLA, the object would be
kpc in size with a flux of Jy in
the F160W filter, implying a luminosity at {\AA} in
the rest frame of L at ,
for . However, no significant H- emission is seen,
suggesting a low star formation rate (SFR) (3 upper limit of 4.0
M yr), or very high dust obscuration.
Alternatively, the object may be associated with the host galaxy of the quasar.
H-band images obtained with the NICMOS camera 2 coronagraph show a much fainter
structure kpc in size and containing four knots of
continuum emission, located 0.7\arcsec away from the quasar. We have probed
regions far closer to the quasar sight-line than in most previous studies of
high-redshift intervening DLAs. The two objects we report mark the closest
detected high-redshift DLA candidates yet to any quasar sight line. If the
features in our images are associated with the DLA, they suggest faint,
compact, somewhat clumpy objects rather than large, well-formed proto-galactic
disks or spheroids.Comment: 52 pages of text, 19 figures, To be published in Astrophysical
Journal (accepted Dec. 8, 1999
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