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Search Results: 1 - 10 of 243270 matches for " James R. Graham "
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An Imaging Fourier Transform Spectrometer for the Next Generation Space Telescope
James R. Graham
Physics , 1999,
Abstract: Due to its simultaneous deep imaging and integral field spectroscopic capability, an Imaging Fourier Transform Spectrograph (IFTS) is ideally suited to the Next Generation Space Telescope (NGST) mission, and offers opportunities for tremendous scientific return in many fields of astrophysical inquiry. We describe the operation and quantify the advantages of an IFTS for space applications. The conceptual design of the Integral Field Infrared Spectrograph (IFIRS) is a wide field (5'.3 x 5'.3) four-port imaging Michelson interferometer.
An Imaging Fourier Transform Spectrometer for NGST
James R. Graham
Physics , 1999,
Abstract: Due to its simultaneous deep imaging and integral field spectroscopic capability, an Imaging Fourier Transform Spectrograph (IFTS) is ideally suited to the Next Generation Space Telescope (NGST) mission, and offers opportunities for tremendous scientific return in many fields of astrophysical inquiry. We describe the operation and quantify the advantages of an IFTS for space applications. The conceptual design of the Integral Field Infrared Spectrograph (IFIRS) is a wide field (5'.3 x 5'.3) four-port imaging Michelson interferometer.
The Spectroscopic Redshift of an Extremely Red Object and the Nature of the Very Red Galaxy Population
James R. Graham,Arjun Dey
Physics , 1996, DOI: 10.1086/178000
Abstract: Infrared surveys have discovered a significant population of bright (K<19) extremely red (R-K>6) objects. Little is known about the properties of these objects on account of their optical faintness (R>24). Here, we report deep infrared imaging and spectroscopy of one of the extremely red objects (EROs) discovered by Hu \& Ridgway (1994) in the field of the z=3.79 quasar PC1643+4631A. The infrared images were obtained in 0.5" seeing, and show that the object (denoted HR10) is not a dynamically relaxed elliptical galaxy dominated by an old stellar population as was previously suspected, but instead has an asymmetric morphology suggestive of either a disk or an interacting system. The infrared spectrum of HR10 shows a single, possibly broad emission feature at 1.60um which we identify as Halpha+[NII] at z=1.44. The luminosity and width of this emission line indicates either intense star formation (about 20h^{-2} solar masses/yr) or the presence of an active nucleus. Based on the rest frame UV-optical spectral energy distribution, the luminosity of HR10 is estimated to be 3 to 8 L*. The colors of HR10 are unusually red for a galaxy (at z=1.44 the age of HR10 is at most 2 to 8 Gyr depending on cosmology), and indicate that HR10 is dusty. HR10 is detected weakly at radio wavelengths; this is consistent with either the starburst or AGN hypothesis. If HR10 is a typical representative of its class, EROs are numerous and represent a significant component of the luminous objects in the Universe at z approx 1.5.
An Infrared Camera for Leuschner Observatory and the Berkeley Undergraduate Astronomy Lab
James R. Graham,Richard R. Treffers
Physics , 2001, DOI: 10.1086/320284
Abstract: We describe the design, fabrication, and operation of an infrared camera which is in use at the 30-inch telescope of the Leuschner Observatory. The camera is based on a Rockwell PICNIC 256 x 256 pixel HgCdTe array, which is sensitive from 0.9-2.5 micron. The primary purpose of this telescope is for undergraduate instruction. The cost of the camera has been minimized by using commercial parts whereever practical. The camera optics are based on a modified Offner relay which forms a cold pupil where stray thermal radiation from the telescope is baffled. A cold, six-position filter wheel is driven by a cryogenic stepper motor, thus avoiding any mechanical feed throughs. The array control and readout electronics are based on standard PC cards; the only custom component is a simple interface card which buffers the clocks and amplifies the analog signals from the array.
High Resolution Infrared Imaging of FSC10214+4724: Evidence for Gravitational Lensing
James R. Graham,Michael C. Liu
Physics , 1995, DOI: 10.1086/309629
Abstract: We present near--infrared observations of the ultraluminous high-redshift (z=2.286) IRAS source FSC 10214+4724 obtained in 0.''4 seeing at the W. M. Keck telescope. These observations show that FSC 10214+4724 consists of a highly symmetric circular arc centered on a second weaker source. The arc has an angular extent of about 140 degrees and is probably unresolved in the transverse direction. This morphology constitutes compelling prima facie evidence for a gravitationally lensed system. Our images also contain evidence for the faint counter image predicted by the lens hypothesis. The morphology of FSC 10214+4724 can be explained in terms of a gravitationally lensed background source if the object at the center of curvature of the arc is an L* galaxy at z ~ 0.4. If FSC 10214+4724 is lensed then there is significant magnification and its luminosity has been overestimated by a large factor. Our results suggest FSC~10214+4724 is not a uniquely luminous object but ranks amo ng the most powerful quasars and ultraluminous IRAS galaxies.
Keck Observations of the Most Distant Galaxy: 8C1435+63 at z=4.25
Hyron Spinrad,Arjun Dey,James R. Graham
Physics , 1994, DOI: 10.1086/187713
Abstract: We report on Keck observations and confirm the redshift of the most distant galaxy known: 8C1435+63 at z=4.25. The spectrum shows a strong Ly$\alpha$ line, a Ly$\alpha$ forest continuum break and a continuum break at $\lambda_{rest}=912$\AA. The Ly$\alpha$ emission is spatially extended and roughly aligned with the radio source. The galaxy shows a double structure in the $I$-band ($\lambda_{rest}\approx$1500\AA) which is aligned with the radio axis; the two $I$-band components spatially coincide with the nuclear and southern radio components. Some fraction of the $I$ band emission could be due to a nonthermal process such as inverse compton scattering. In the $K$-band ($\lambda_{rest}\approx$4200\AA), which may be dominated by starlight, the galaxy has a very low surface brightness, diffuse morphology. The $K$ morphology shows little relationship to the radio source structure, although the major axis of the $K$ emission is elongated roughly in the direction of the radio source axis. The galaxian continuum is very red ($I-K>4$) and if the $K$ continuum is due to starlight, implies a formation redshift of $z_f > 5$. We speculate that this galaxy may be the progenitor of a present day cD galaxy.
Tracing the Dynamics of Disk Galaxies with Optical and IR Surface Photometry: Color Gradients in M99
Rosa A. Gonzalez,James R. Graham
Physics , 1995, DOI: 10.1086/176999
Abstract: We present optical and IR surface photometry of M99 (NGC 4254) at g, r_S i, J and K'. We also present a K' image of M51 (NGC 5194) for comparison. Fourier decomposition of the disk light reveals that the radial distribution of power depends on wavelength, which in turn implies that the spiral structure traced in the visual (i.e. young population I and dust) is different from the one detected at 2 microns (i.e. old stellar disk). We observe radial modulation of the power and a dependency of power with wavelength that are consistent with modal theory of spiral structure. A central motivation for our research is the fundamental idea of density wave theory that the passage of a spiral density wave triggers star formation. We have found a stellar population age gradient consistent with this scenario in a reddening-free, red supergiant-sensitive, Q-like photometric parameter at 6 kpc galactocentric distance across one of the arms of M99. We rule out that the change in this parameter, Q(r_SJgi), across the arm is mainly due to dust. The difference in Q(r_SJgi) going from the interarm regions to the arms also indicates that arms cannot be due exclusively to crowding of stellar orbits. We present the first measurement of Omega_p, the angular speed of the spiral pattern, and of the location of the corotation radius, derived from the drift velocity of the young stars away from their birth site. The measured Q(r_SJgi) implies a star formation rate for M99 within the range of 10-20 M_odot/yr; a disk stellar mass surface density of ~80 M_odot/pc^2; and a maximum contribution of ~20 percent from red supergiants to the K' light in a small region, and much smaller on average. We measure a K' arm--interarm contrast of 2-3, too high for M99 to be a truly isolated galaxy.
Infrared Surface Brightness Fluctuations of the Coma Elliptical NGC 4874 and the Value of the Hubble Constant
Michael C. Liu,James R. Graham
Physics , 2001, DOI: 10.1086/323174
Abstract: We have used the Keck I Telescope to measure K-band surface brightness fluctuations (SBFs) of NGC 4874, the dominant elliptical galaxy in the Coma cluster. We use deep HST WFPC2 optical imaging to account for the contamination due to faint globular clusters and improved analysis techniques to derive measurements of the SBF apparent magnitude. Using a new SBF calibration which accounts for the dependence of K-band SBFs on the integrated color of the stellar population, we measure a distance modulus of 34.99+/-0.21 mag (100+/-10 Mpc) for the Coma cluster. The resulting value of the Hubble constant is 71+/-8 km/s/Mpc, not including any systematic error in the HST Cepheid distance scale.
Shocking Clouds in the Cygnus Loop
N. A. Levenson,James R. Graham
Physics , 2001, DOI: 10.1086/322502
Abstract: With Hubble Space Telescope Wide-Field Planetary Camera 2 observations of the Cygnus Loop supernova remnant, we examine the interaction of an interstellar cloud with the blast wave on physical scales of 10^15 cm. The shock front is distorted, revealing both edge-on and face-on views of filaments and diffuse emission, similar to those observed on larger scales at lower resolution. We identify individual shocks in the cloud of density n~15 cm^-3 having velocity v_s~170 km/s. We also find the morphologically unusual diffuse Balmer-dominated emission of faster shocks in a lower-density region. The obstacle diffracts these shocks, so they propagate at oblique angles with respect to the primary blast wave. The intricate network of diffuse and filamentary H alpha emission arises during the early stage of interaction between the cloud and blast wave, demonstrating that complex shock propagation and emission morphology occur before the onset of instabilities that destroy clouds completely.
Near-IR Spectroscopy and Population Synthesis of Super Star Clusters in NGC 1569
Andrea M. Gilbert,James R. Graham
Physics , 2000,
Abstract: We present H- and K-band NIRSPEC spectroscopy of super star clusters (SSCs) in the irregular starburst galaxy NGC 1569, obtained at the Keck Observatory. We fit these photospheric spectra to NextGen model atmospheres to obtain effective spectral types of clusters, and find that the information in both H- and K-band spectra is necessary to remove degeneracy in the fits. The light of SSC B is unambiguously dominated by K0 supergiants (T_eff=4400 +- 100 K, log g=0.5 +- 0.5). The double cluster SSC A has higher T_eff (G5) and less tightly constrained surface gravity (log g=1.3 +- 1.3), consistent with a mixed stellar population dominated by blue Wolf-Rayet stars and red supergiants. We predict the time evolution of infrared spectra of SSCs using Starburst99 population synthesis models coupled with empirical stellar spectral libraries (at solar metallicity). The resulting model sequence allows us to assign ages of 15-18 Myr for SSC B and 18-21 Myr for SSC A.
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