Article: The host galaxy of GRB 990123[Show abstract] [Hide abstract] ABSTRACT: We present deep images of the field of GRB 990123 obtained in a broadband UV/visible bandpass with the Hubble Space Telescope (HST) and deep near-infrared images obtained with the Keck I 10 m telescope. The HST image reveals that the optical transient (OT) is offset by 067 (5.8 kpc in projection) from an extended, apparently interacting galaxy. This galaxy, which we conclude is the host galaxy of GRB 990123, is the most likely source of the absorption lines of metals at a redshift of z=1.6 seen in the spectrum of the OT. With magnitudes of Gunn-r = 24.5 ± 0.2 and K = 22.1±0.3 mag, this corresponds to an L ~ 0.5L galaxy, assuming that it is located at z = 1.6. The estimated unobscured star formation rate is ≈4 M☉ yr−1, which is typical for normal galaxies at comparable redshifts. There is no evidence for strong gravitational lensing magnification of this burst, and some alternative explanation for its remarkable energetics (such as beaming) may therefore be required. The observed offset of the OT from the nominal host center, the absence of broad absorption lines in the afterglow spectrum, and the relatively blue continuum of the host do not support the notion that gamma-ray bursts (GRBs) originate from active galactic nuclei or massive black holes. Rather, the data are consistent with models of GRBs that involve the death and/or merger of massive stars. Indeed, the HST image suggests an intimate connection between GRB 990123 and a star-forming region.
- [Show abstract] [Hide abstract] ABSTRACT: We use NIRSPEC, a near-IR spectrometer on Keck II, to obtain moderate-resolution (R = 1540) spectroscopy that shows conclusively that the C IV emission line in the z = 5.74 quasar SDSSp J104433.04-012502.2 is accompanied by broad, blueshifted C IV absorption. The line has a "balnicity index" of 900 km s-1 and a rest-frame equivalent width of 13.1 ± 1.3 Å relative to the continuum. This confirms its membership in the class of objects called "broad absorption line" (BAL) quasi-stellar objects (QSOs). SDSSp J1044-0125 was previously suggested to be a BAL QSO based on its UV-to-X-ray flux ratio, which is larger than most non-BAL QSOs. The C IV emission is of normal strength, implying a metallicity similar to that found in other, lower redshift, QSOs.
- [Show abstract] [Hide abstract] ABSTRACT: We present follow-up optical g', r', and i' imaging and spectroscopy of serendipitous X-ray sources detected in six archival Chandra images included in the Chandra Multiwavelength Project (ChaMP). Of the 486 X-ray sources detected between 3 × 10-16 and 2 × 10-13 (with a median flux of 3 × 10-15) ergs cm-2 s-1, we find optical counterparts for 377 (78%), or 335 (68%) counting only unique counterparts. We present spectroscopic classifications for 125 objects, representing 75% of sources with r* < 21 optical counterparts (63% to r* = 22). Of all classified objects, 63 (50%) are broad-line active galactic nuclei (AGNs), which tend to be blue in (g*-r*) colors. X-ray information efficiently segregates these quasars from stars, which otherwise strongly overlap in these SDSS colors until z > 3.5. We identify 28 sources (22%) as galaxies that show narrow emission lines, while 22 (18%) are absorption line galaxies. Eight galaxies lacking broad-line emission have X-ray luminosities that require they host an AGN (logLX > 43). Half of these have hard X-ray emission suggesting that high gas columns obscure both the X-ray continuum and the broad emission line regions. We find objects in our sample that show signs of X-ray or optical absorption, or both, but with no strong evidence that these properties are coupled. ChaMP's deep X-ray and optical imaging enable multiband selection of small and/or high-redshift groups and clusters. In these six fields we have discovered three new clusters of galaxies, two with z > 0.4, and one with photometric evidence for a similar redshift.
- [Show abstract] [Hide abstract] ABSTRACT: We present the first science results from the Keck Interferometer, a direct-detection infrared interferometer utilizing the two 10 m Keck telescopes. The instrument and system components are briefly described. We then present observations of the T Tauri object DG Tau, which is resolved by the interferometer. The resolved component has a radius of 0.12-0.24 AU, depending on the assumed stellar and extended component fluxes and the model geometry used. Possible origins and implications of the resolved emission are discussed.
- [Show abstract] [Hide abstract] ABSTRACT: The organic volatile composition of the long-period comet C/1999 H1 (Lee) was investigated using the first of a new generation of cross-dispersed cryogenic infrared spectrometers (NIRSPEC, at the Keck Observatory atop Mauna Kea, HI). On 1999 August 19-21 the organics spectral region (2.9-3.7 μm) was completely sampled at both moderate and high dispersion, along with the CO fundamental region (near 4.67 μm), revealing emission from water, carbon monoxide, methanol, methane, ethane, acetylene, and hydrogen cyanide. Many new multiplets from OH in the 1-0 band were seen in prompt emission, and numerous new spectral lines were detected. Several spectral extracts are shown, and global production rates are presented for seven parent volatiles. Carbon monoxide is strongly depleted in comet Lee relative to comets Hyakutake and Hale-Bopp, demonstrating that chemical diversity occurred in the giant-planets' nebular region.
Article: An FeLoBAL binary quasar[Show abstract] [Hide abstract] ABSTRACT: In an ongoing infrared imaging survey of quasars at the Keck Observatory, we have discovered that the z = 1.285 quasar SDSS J233646.2-010732.6 comprises two point sources with a separation of 167. Resolved spectra show that one component is a standard quasar with a blue continuum and broad emission lines; the other is a broad absorption line (BAL) quasar, specifically, a BAL QSO with prominent absorption from Mg II and metastable Fe II, making it a member of the "FeLoBAL" class. The number of known FeLoBALs has recently grown dramatically from a single example to more than a dozen, including a gravitationally lensed example and the binary member presented here, suggesting that this formerly rare object may be fairly common. Additionally, the presence of this BAL quasar in a relatively small separation binary adds to the growing evidence that the BAL phenomenon is not due to viewing a normal quasar at a specific orientation but rather that it is an evolutionary phase in the life of many, if not all, quasars and is particularly associated with conditions found in interacting systems.
- [Show abstract] [Hide abstract] ABSTRACT: We report the discovery of a radio transient VLA 232937.2-235553, coincident with the proposed X-ray afterglow for the gamma-ray burst GRB 981226. This gamma-ray burst (GRB) has the highest ratio of X-ray to gamma-ray fluence of all the GRBs detected by BeppoSAX so far, and yet no corresponding optical transient was detected. The radio light curve of VLA 232937.2-235553 is qualitatively similar to that of several other radio afterglows. At the subarcsecond position provided by the radio detection, optical imaging reveals an extended R = 24.9 mag object, which we identify as the host galaxy of GRB 981226. Afterglow models that invoke a jetlike geometry for the outflow or that require an ambient medium with a radial density dependence, such as that produced by a wind from a massive star, are both consistent with the radio data. Furthermore, we show that the observed properties of the radio afterglow can explain the absence of an optical transient without the need for large extinction local to the GRB.
- [Show abstract] [Hide abstract] ABSTRACT: With the recent release of large (i.e., 100 million objects), well-calibrated photometric surveys, such as Digitized Palomar Observatory Sky Survey (DPOSS), Two Micron All Sky Survey, and Sloan Digital Sky Survey, spectroscopic identification of important targets is no longer a simple issue. In order to enhance the returns from a spectroscopic survey, candidate sources are often preferentially selected to be of interest, such as brown dwarfs or high-redshift quasars. This approach, while useful for targeted projects, risks missing new or unusual species. We have, as a result, taken the alternative path of spectroscopically identifying interesting sources with the sole criterion being that they are in low-density areas of the g-r and r-i color space defined by DPOSS. In this paper, we present three peculiar broad absorption line quasars that were discovered during this spectroscopic survey, demonstrating the efficacy of this approach. PSS J0052+2405 is an iron low-ionization broad absorption line (LoBAL) quasar at a redshift z = 2.4512 ± 0.0001 with very broad absorption from many species. PSS J0141+3334 is a reddened LoBAL quasar at z = 3.005 ± 0.005 with no obvious emission lines. PSS J1537+1227 is an iron LoBAL at a redshift of z = 1.212 ± 0.007 with strong narrow Mg II and Fe II emission. Follow-up high-resolution spectroscopy of these three quasars promises to improve our understanding of BAL quasars. The sensitivity of particular parameter spaces, in this case a two-color space, to the redshift of these three sources is dramatic, raising questions about traditional techniques of defining quasar populations for statistical analysis.
- [Show abstract] [Hide abstract] ABSTRACT: The results of spectroscopic observations of 202 stellar objects, and photometric observations of 171, from the Second Byurakan Survey (SBS) are reported. The SBS sample has proved to be a rich source of newly identified quasars, Seyfert-type galaxies, degenerate stars, and hot subdwarfs. In this subsample we have identified 71 new QSOs; one BL Lacertae object; one Seyfert 1 galaxy; one LINER; one blue compact galaxy; 31 white dwarfs (WDs), 25 of DA type and six of DB type; 26 subdwarfs; 11 horizontal-branch B-type, 11 normal/horizontal-branch, 18 G-type, and 11 F-type stars; 10 objects with composite spectra; two cataclysmic variables; and six objects with continuous spectra. Among the 71 QSOs, we have found three broad absorption line QSOs, namely, SBS 1139+534, 1524+517, and 1524+491, and one damped Lyα QSO, SBS 1425+606. The very luminous objects have visual magnitudes in the range 15.9 < V < 16.9, redshifts 2.667 < z < 3.170, and luminosities -30.5 > MV > -31.5. A number of the low-redshift SBS QSOs show strong Fe II complexes at rest wavelengths of 4570, 5190, and 5320 Å. We present accurate positions, spectral classifications, and magnitudes for all objects. The redshifts, equivalent widths, and spectra for QSOs and emission-line galaxies are given, as are some typical spectra for hot stars. The vast majority (63%) of stellar objects selected in the SBS turned out to be WDs (36%) and sdB subdwarfs (27%). Only ~5%–7% of objects with B < 16.4 and ~13% with B ~ 17.0 were identified as QSOs. In total, 470 QSOs and ~500 hot stars were discovered in the course of the SBS. The lower limit on the surface density of bright QSOs in the redshift range 0.3 < z < 2.2 is no fewer than 0.06 deg-2 for B < 17.0 and 0.13 deg-2 for B < 17.5. The surface density of DA WDs is estimated to be 0.06 deg-2 for B < 16.0 and 0.14 deg-2 for B < 17.0.
- [Show abstract] [Hide abstract] ABSTRACT: This study focuses on some of the most metal-poor damped Lyman alpha absorbers known in the spectra of high redshift QSOs, using new and archival observations obtained with UV-sensitive echelle spectrographs on the Keck and VLT telescopes. The weakness and simple velocity structure of the absorption lines in these systems allows us to measure the abundances of several elements, and in particular those of C, N, and O, a group that is difficult to study in DLAs of more typical metallicities. We find that when the oxygen abundance is less than about 1/100 of solar, the C/O ratio in high redshift DLAs and sub-DLAs matches that of halo stars of similar metallicity and shows higher values than expected from galactic chemical evolution models based on conventional stellar yields. Furthermore, there are indications that at these low metallicities the N/O ratio may also be above simple expectations and may exhibit a minimum value, as proposed by Centurion and her collaborators in 2003. Both results can be interpreted as evidence for enhanced production of C and N by massive stars in the first few episodes of star formation, in our Galaxy and in the distant proto-galaxies seen as QSO absorbers. The higher stellar yields implied may have an origin in stellar rotation which promotes mixing in the stars' interiors, as considered in some recent model calculations. We briefly discuss the relevance of these results to current ideas on the origin of metals in the intergalactic medium and the universality of the stellar initial mass function. Comment: 17 pages, 9 Figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society
- [Show abstract] [Hide abstract] ABSTRACT: Using the high-quality data set of 165 images taken at 11 epochs over the 5.13 h rotation of the large C-type Asteroid 511 Davida, we find the dimensions of its triaxial ellipsoid model to be 357±2×294±2×231±50 km. The images were acquired with the adaptive optics system on the 10 m Keck II telescope on December 27, 2002. The a and b diameters are much better determined than previously estimated from speckle interferometry and indirect measurements, and our mean diameter, (abc)1/3=289±21 km, is 19% below previous estimates. We find the pole to lie within 2° of [RA=295°; Dec=0°] or in Ecliptic coordinates [λ=297°; β=+21°], a significant improvement to the pole direction. Otherwise, previous determinations of the axial ratios agree with our new results. These observations illustrate that our technique of finding the dimensions and pole of an asteroid from its changing projected size and shape is very powerful because it can be done in essentially one night as opposed to decades of lightcurves. Average departures of 3% (5 km) of the asteroid's mean radius from a smooth outline are detected, with at least two local positive-relief features and at least one flat facet showing approximately 15 km deviations from the reference best-fit ellipsoid. The facet is reminiscent of large global-scale craters on Asteroid 253 Mathilde (also a C-type) when seen edge-on in close-up images from the NEAR mission flyby. We show that giant craters (up to 150 km diameter, the size of the largest facets seen on Davida) can be expected from the impactor size distribution, without likelihood of catastrophic disruption of Davida.
- [Show abstract] [Hide abstract] ABSTRACT: Keck AO observations of three asteroids have been analyzed to extract limb profiles. We identify a large facet on 511 Davida that may be the signature of giant craters seen edge-on, reminiscent of those seen on Mathilde. Preliminary analysis shows that si
- [Show abstract] [Hide abstract] ABSTRACT: We present 1.6-4.7 $\mu$m images of PPNe and young PNe recently obtained with the Keck Adaptive Optics (AO) system. These observations provide higher angular resolution and probe deeper into the dusty envelopes of post-AGB objects than HST images and, therefore, show with unprecedented detail the morphology of these nebulae. Some objects have limb-brightened lobes displaying a remarkable point-like symmetry, which suggests the presence of underlying precessing jets that may be carving out the nebular lobes. Our images also show a very rich structure at the very small scale of $\sim$0.” 1, including jet-like features, arcs, searchlight beams, as well as faint, extended halos in a number of objects.
- [Show abstract] [Hide abstract] ABSTRACT: Here we report successful interferometric coupling of two large telescopes with single-mode fibers. Interference fringes were obtained in the 2- to 2.3-micrometer wavelength range on the star 107 Herculis by using the two Keck 10-meter telescopes, each feeding their common interferometric focus with 300 meters of single-mode fibers. This experiment demonstrates the potential of fibers for future kilometric arrays of telescopes and is the first step toward the 'OHANA (Optical Hawaiian Array for Nanoradian Astronomy) interferometer at the Mauna Kea observatory in Hawaii. It opens the way to sensitive optical imagers with resolutions below 1 milli‐arc second. Our experimental setup can be directly extended to large telescopes separated by many hundreds of meters.
Conference Paper: Rotation and Morphology of Asteroid 511 Davida[Show abstract] [Hide abstract] ABSTRACT: We present spatially resolved images of asteroid 511 Davida, one of ten large main belt asteroids imaged during the course of our Resolved Asteroid Program. We compare the shape, pole orientation, and size to measurements obtained by other methods.
- [Show abstract] [Hide abstract] ABSTRACT: We present outflow velocity measurements of the BAL QSO 1303+308 taken over more than a twenty year baseline. This object exhibits complex absorption troughs in its near UV spectrum that are highly structured, containing a number of individual, resolved absorption doublets. Furthermore, a number of the absorption features have been reported to be `line-locked' with the longer wavelength member of one doublet being coincident with the shorter wavelength member of another. Although detailed models are lacking, these coincidences have been used to infer that radiative acceleration plays a role in the dynamics of the absorbing gas. Observations of Q1303+308 were made in the 1980s and 1990s with the MMT spectrograph at a resolution of 60 km/sec and in the 21st century with HIRES on Keck I at a resolution of 5 km/sec. The elapsed time in the rest frame of the QSO (z=1.76) is approximately eight years. By comparing the N V, Si IV and C IV absorption complexes, we are able to set extremely stringent limits on the secular acceleration of the outflowing material. We also comment on changes in the equivalent widths of the absorption troughs over the elapsed time of the observations.
- [Show abstract] [Hide abstract] ABSTRACT: We present the spatially resolved velocity structure of the V723 Cas nova shell. Strong coronal emission lines of [Si VI] and [Al IX] are present in the expanding shell. Brgamma is detected but not spatially resolved which implies that hydrogen recombination emission is absent in the nova shell. The PSF/continuum subtracted data cubes reveal the morphology of the nova shell in 3 dimensions. The shell is slightly elliptical with a semi-major axis of 0.35 arcsec or 1200 AU using a distance of 3.5 kpc. We selected V723 Cas in this pilot study of nova shells since it showed double-peaked coronal line emission in NIRSPEC spectra from 2004 (presented here). Additionally, the shell has continued to expand since it was unresolved in a 1998 HST+NICMOS study. The intervening 7 years and coronal emission made V723 Cas an ideal candidate for the unprecedented spatial resolution in the infrared provided by OSIRIS with LGSAO on Keck II.
- [Show abstract] [Hide abstract] ABSTRACT: On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics.
W. M. Keck ObservatoryHilo, Hawaii, United States
California Institute of TechnologyPasadena, California, United States
The University of Arizona
Tucson, Arizona, United States
- Department of Astronomy