664 research outputs found
Research at Palomar Observatory in planetary astronomy
A wide range of observational studies are carried out to improve our understanding of the bodies of the outer solar system. Using the 200-inch Hale telescope, near-infrared observations are made of Uranus, Neptune, and the Pluto-Charon system. High time resolution occultation observations of the Uranus Ring system are used to study in detail the dynamics of this system. Occultation studies of Neptune are probing this intriguing ring-arc system. Occulation observations of the Pluto-Charon system probe the surface properties of these distant bodies. In addition, the plate material of the PSSII servey is being used to search for new comets and asteroids. Researchers observed one Neptune stellar occultation in July 1987 and completed the analysis of a series of seven separate Neptune occultation observations in conjunction with Nicholson et al., of Cornell. The analysis has shown that minimum of three ring arcs, at radii ranging from 54,000 km - 67,000 km are required to account for the high quality ring events. Current theoretical models can account for these data. Of two observations scheduled of Pluto-Charon mutual occulations scheduled for the 200-inch, the Charon eclipse event was successfully observed (the other was clouded out)
Optical Spectroscopy of K-selected Extremely Red Galaxies
We have obtained spectroscopic redshifts for 24 red galaxies from a sample
with median Ks=18.7 and F814W - Ks > 4, using the Keck telescope. These
EROshave high resolution morphologies from HST (Yan & Thompson 2003). Among the
24 redshifts, the majority (92%) are at . We derived the
rest-frame J-band luminosity function at . Our result
suggests that the luminosity evolution between bright EROs at and the
present-day L massive galaxies is at most about 0.7 magnitude. Combining
the morphologies and deep spectroscopy revealed the following properties: (1)
86% of the spectra have absorption features from old stars, suggesting that the
dominant stellar populations seen in the rest-frame UV are old stars. 50% of
the sources have pure absorption lines, while the remaining 50% have emission
lines, indicating recent star formation. We conclude that the color criterion
for EROs is very effective in selecting old stellar populations at ,
and a large fraction of these systems with prominent old stellar populations
also have recent star formation. (2) The 12 emission line systems have the same
number of disk and bulge galaxies as in the remaining 12 pure absorption line
systems. We conclude that spectral classes do not have a simple, direct
correspondence with morphological types. (3) Three EROs could be isolated, pure
passively evolving early-type galaxies at . This implies that only a
small fraction (10%--15%) of early-type galaxies are formed in a rapid burst of
star formation at high redshifts and evolved passively since then. (Abridged).Comment: 27 pages, 8 figures. Accepted for publication in Astronomical
Journal, issue March 200
Infrared astronomy research and high altitude observations
Highlights are presented of studies of the emission mechanisms in the 4 to 8 micron region of the spectrum using a circular variable filter wheel spectrometer with a PbSnTe photovoltaic detector. Investigations covered include the spectroscopy of planets, stellar atmospheres, highly obscured objects in molecular clouds, planetary nebulae, H2 regions, and extragalactic objects
Near-threshold high-order harmonic spectroscopy with aligned molecules
We study high-order harmonic generation in aligned molecules close to the
ionization threshold. Two distinct contributions to the harmonic signal are
observed, which show very different responses to molecular alignment and
ellipticity of the driving field. We perform a classical electron trajectory
analysis, taking into account the significant influence of the Coulomb
potential on the strong-field-driven electron dynamics. The two contributions
are related to primary ionization and excitation processes, offering a deeper
understanding of the origin of high harmonics near the ionization threshold.
This work shows that high harmonic spectroscopy can be extended to the
near-threshold spectral range, which is in general spectroscopically rich.Comment: 4 pages, 4 figure
Mode-selective coupling of coherent phonons to the Bi2212 electronic band structure
Cuprate superconductors host a multitude of low-energy optical phonons. Using
time- and angle-resolved photoemission spectroscopy, we study coherent phonons
in BiSrCaYCuO. Sub-meV
modulations of the electronic band structure are observed at frequencies of
and THz. For the dominant mode at 3.94 THz, the
amplitude of the band energy oscillation weakly increases as a function of
momentum away from the node. Theoretical calculations allow identifying the
observed modes as CuO-derived phonons. The Bi- and Sr-derived
modes which dominate Raman spectra in the relevant frequency range are
absent in our measurements. This highlights the mode-selectivity for phonons
coupled to the near-Fermi-level electrons, which originate from CuO
planes and dictate thermodynamic properties.Comment: 7 pages, 3 figure
The IRAS bright galaxy sample. V. Multibeam photometry of galaxies with L(IR) ⩾ 10^(11) L_☉
Forty-seven galaxies from the IRAS Bright Galaxy Sample with infrared luminosities L_(IR)⩾ 10^(11) L_☉ have been measured at 1.3, 1.65, and 2.2 µm with beam diameters of 17", 33", and 55". These measurements, combined with 5" and 10" observations presented in an earlier paper, provide an opportunity to study the spatial distribution of the near-infrared emission in luminous IRAS galaxies. It is found that the unusually red near-infrared colors known previously for many of these galaxies are confined to the nuclear regions, whereas the outer disk regions have near-infrared colors essentially appropriate for a
normal stellar population. Since dust reddening and emission are required to explain the unusual nuclear
colors, it follows that the observed effects of dust in these galaxies are also confined primarily to the nuclei. Thus, it is probable that the far-infrared emission, the bulk of the entire luminosity in infrared luminous galaxies, is highly concentrated about the nuclei, and that the physical processes responsible for the unusual properties of infrared luminous galaxies tend to occur within the central regions, with diameters ≾1-3 kpc. The nuclei are found to have considerably higher 2.2 µm luminosities than are found in classical “starburst” nuclei, implying that infrared luminous galaxies are characterized by extremely high radiation densities in their central regions, presumably due to intense star formation activity and/or the presence of a dust-enshrouded quasar. However, the nuclei of the galaxies
studied are typically not as luminous at 2.2 µm as classical Seyfert nuclei, which may be partly attributable
to extinction from dust at near-infrared wavelengths, particularly for those sources in the sample that have been identified in the literature as having Seyfert nuclei. Finally, the large diameter beam measurements are used to obtain estimates of the total near-infrared emission. It is found that, since most of the infrared luminosity is coming from the nuclei, the global near-infrared properties of infrared luminous galaxies are not good tracers of infrared activity. Also, the contribution from the observed stellar emission to the total observed luminosity is found to be ≾25% for most of the galaxies in the sample, considerably smaller than the value for typical low-luminosity spiral galaxies
Cosmic Evolution of a Sample of Infrared Luminous Galaxies
A sample of faint, southern-hemisphere 60 μm sources
(f_(60) > 100mJy) detected as part of the IRAS Additional Observations has been used, in conjunction with CCD imaging, to produce a list of faint infrared galaxies. Redshifts of this sample of galaxies can be compared
with model predictions for several evolutionary scenarios; the comparisons show an excess of galaxies at higher redshifts (z > 0.1) compared with the predictions of models which assume no evolution of the infrared-galaxy luminosity function
The Compact Nucleus of the Deep Silicate Absorption Galaxy NGC 4418
High resolution, Hubble Space Telescope (HST) near-infrared and Keck
mid-infrared images of the heavily extinguished, infrared luminous galaxy NGC
4418 are presented. These data make it possible to observe the imbedded
near-infrared structure on scales of 10-20 pc, and to constrain the size of the
mid-infrared emitting region. The 1.1-2.2 um data of NGC 4418 show no clear
evidence of nuclear star clusters or of a reddened active galactic nucleus.
Instead, the nucleus of the galaxy consists of a ~100-200 pc linear structure
with fainter structures extending radially outward. The near-infrared colors of
the linear feature are consistent with a 10-300 Myr starburst suffering
moderate levels (few magnitudes) of visual extinction. At 7.9-24.5 um, NGC 4418
has estimated size upper limits in the range of 30-80 pc. These dimensions are
consistent with the highest resolution radio observations obtained to date of
NGC 4418, as well as the size of 50-70 pc expected for a blackbody with a
temperature derived from the 25 um, 60 um, and 100 um flux densities of the
galaxy. Further, a spectral energy distribution constructed from the
multi-wavelength mid-infrared observations show the strong silicate absorption
feature at 10 um, consistent with previous mid-infrared observations of NGC
4418. An infrared surface brightness of 2.1x10^13 L_sun kpc^-2 is derived for
NGC 4418. Such a value, though consistent with the surface brightness of warm
ultraluminous infrared galaxies (ULIGs: L_IR [8-1000 um] >~ 10^12 L_sun) such
as IRAS 05189-2524 and IRAS 08572+3915, is not large enough to distinguish NGC
4418 as a galaxy powered by an Active Galactic Nucleus (AGN), as opposed to a
lower surface brightness starburst.Comment: LaTex, 7 pages, including 2 jpg figures and 3 postscript figures, AJ,
in press (May, 2003
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