Showing papers in "Publications of the Astronomical Society of the Pacific in 2003"

Galactic stellar and substellar initial mass function

Abstract: We review recent determinations of the present-day mass function (PDMF) and initial mass function (IMF) in various components of the Galaxy—disk, spheroid, young, and globular clusters—and in conditions characteristic of early star formation. As a general feature, the IMF is found to depend weakly on the environment and to be well described by a power-law form forM , and a lognormal form below, except possibly for m!1 early star formation conditions. The disk IMF for single objects has a characteristic mass around M , m!0.08 c and a variance in logarithmic mass , whereas the IMF for multiple systems hasM , and . j!0.7 m!0.2 j!0.6 c The extension of the single MF into the brown dwarf regime is in good agreement with present estimates of L- and T-dwarf densities and yields a disk brown dwarf number density comparable to the stellar one, n!n! BD " pc !3 .T he IMF of young clusters is found to be consistent with the disk fi eld IMF, providing the same correction 0.1 for unresolved binaries, confirming the fact that young star clusters and disk field stars represent the same stellar population. Dynamical effects, yielding depletion of the lowest mass objects, are found to become consequential for ages!130 Myr. The spheroid IMF relies on much less robust grounds. The large metallicity spread in the local subdwarf photometric sample, in particular, remains puzzling. Recent observations suggest that there is a continuous kinematic shear between the thick-disk population, present in local samples, and the genuine spheroid one. This enables us to derive only an upper limit for the spheroid mass density and IMF. Within all the uncertainties, the latter is found to be similar to the one derived for globular clusters and is well represented also by a lognormal form with a characteristic mass slightly larger than for the disk, M , ,e xcluding as ignif icant population of m!0.2-0.3 c brown dwarfs in globular clusters and in the spheroid. The IMF characteristic of early star formation at large redshift remains undetermined, but different observational constraints suggest that it does not extend below!1M , .T hese results suggest a characteristic mass for star formation that decreases with time, from conditions prevailing at large redshift to conditions characteristic of the spheroid (or thick disk) to present-day conditions.Theseconclusions,however, remain speculative, given the large uncertainties in the spheroid and early star IMF determinations. These IMFs allow a reasonably robust determination of the Galactic present-day and initial stellar and brown dwarf contents. They also have important galactic implications beyond the Milky Way in yielding more accurate mass-to-light ratio determinations. The mass-to-light ratios obtained with the disk and the spheroid IMF yield values 1.8-1.4 times smaller than for a Salpeter IMF, respectively, in agreement with various recent dynamical determinations. This general IMF determination is examined in the context of star formation theory. None of the theories based on a Jeans-type mechanism, where fragmentation is due only to gravity, can fulfill all the observational constraints on star formation and predict a large number of substellar objects. On the other hand, recent numerical simulations of compressible turbulence, in particular in super-Alfvenic conditions, seem to reproduce both qualitatively and quantitatively the stellar and substellar IMF and thus provide an appealing theoretical foundation. In this picture, star formation is induced by the dissipation of large-scale turbulence to smaller scales through radiative MHD shocks, producing filamentary structures. These shocks produce local nonequilibrium structures with large density contrasts, which collapse eventually in gravitationally bound objects under the combined influence of turbulence and gravity. The concept of a single Jeans mass is replaced by a distribution of local Jeans masses, representative of the lognormal probability density function of the turbulent gas. Objects below the mean thermal Jeans mass still have a possibility to collapse, although with a decreasing probability.

GLIMPSE. I. An SIRTF Legacy Project to Map the Inner Galaxy

Abstract: The Galactic Legacy Infrared Mid‐Plane Survey Extraordinaire (GLIMPSE), a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, will be a fully sampled, confusion‐limited infrared survey of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} ormalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\frac{2}{3}$ \end{document} of the inner Galactic disk with a pixel resolution of ∼1 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \u...

SpeX: A Medium‐Resolution 0.8–5.5 Micron Spectrograph and Imager for the NASA Infrared Telescope Facility

Abstract: We present the design, construction, and performance of SpeX, a medium-resolution 0.8-5.5 mm cryogenic spectrograph and imager, now in operation at the 3.0 m NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The design uses prism cross-dispersers and gratings to provide resolving powers up to R ∼ 2000 simultaneously across 0.8-2.4, 1.9-4.2, or 2.4-5.5 mm, with a 15 long slit. A high-throughput low-resolution prism mode is also provided for faint-object and occultation spectroscopy. Single-order 60 long-slit R ∼ 200 modes with resolving powers up to are available for extended objects. The spectrograph employs an R ∼ 2000

SINGS: The SIRTF Nearby Galaxies Survey

Abstract: The SIRTF Nearby Galaxy Survey is a comprehensive infrared imaging and spectroscopic survey of 75 nearby galaxies. Its primary goal is to characterize the infrared emission of galaxies and their principal infrared-emitting components, across a broad range of galaxy properties and star formation environments. SINGS will provide new insights into the physical processes connecting star formation to the interstellar medium properties of galaxies and provide a vital foundation for understanding infrared observations of the distant universe and ultraluminous and active galaxies. The galaxy sample and observing strategy have been designed to maximize the scientific and archival value of the data set for the SIRTF user community at large. The SIRTF images and spectra will be supplemented by a comprehensive multiwavelength library of ancillary and complementary observations, including radio continuum, H i, CO, submillimeter, BVRIJHK ,H a ,P aa, ultraviolet, and X-ray data. This paper describes the main astrophysical issues to be addressed by SINGS, the galaxy sample and the observing strategy, and the SIRTF and other ancillary data products.

A Method of Correcting Near‐Infrared Spectra for Telluric Absorption*

Abstract: We present a method for correcting near-infrared medium-resolution spectra for telluric absorption. The method makes use of a spectrum of an A0 V star, observed near in time and close in air mass to the target object, and a high-resolution model of Vega, to construct a telluric correction spectrum that is free of stellar absorption features. The technique was designed specifically to perform telluric corrections on spectra obtained with SpeX, a 0.8-5.5 mm medium-resolution cross-dispersed spectrograph at the NASA Infrared Telescope Facility, and uses the fact that for medium resolutions there exist spectral regions uncontaminated by atmospheric absorption lines. However, it is also applicable (in a somewhat modified form) to spectra obtained with other near-infrared spectrographs. An IDL-based code that carries out the procedures is available for downloading via the World Wide Web.

SWIRE: The SIRTF Wide‐Area Infrared Extragalactic Survey

Abstract: The SIRTF Wide‐Area Infrared Extragalactic Survey (SWIRE), the largest SIRTF Legacy program, is a wide‐area imaging survey to trace the evolution of dusty, star‐forming galaxies, evolved stellar populations, and active galactic nuclei (AGNs) as a function of environment, from redshifts to the current epoch. SWIRE will survey seven high‐latitude fields, totaling 60–65 deg2 in all seven SIRTF bands: Infrared Array Camera (IRAC) 3.6, 4.5, 5.6, and 8 μm and Multiband Imaging Photometer for SIRTF (MIPS) 24, 70, and 160 μm. Extensive modeling suggests that the Legacy Extragalactic Catalog may contain in excess of 2 million IR‐selected galaxies, dominated by (1) ∼150,000 luminous infrared galaxies (LIRGs; LFIR > 1011 L⊙) detected by MIPS (and significantly more detected by IRAC), ∼7000 of these with ; (2) 1 million IRAC‐detected early‐type galaxies (∼ with and ∼10,000 with ); and (3) ∼20,000 classical AGNs detected with MIPS, plus significantly more dust‐obscured quasi‐stellar objects/AGNs among the LIRGs. SWIRE will provide an unprecedented view of the evolution of galaxies, structure, and AGNs. The key scientific goals of SWIRE are (1) to determine the evolution of actively star forming and passively evolving galaxies in order to understand the history of galaxy formation in the context of cosmic structure formation; (2) to determine the evolution of the spatial distribution and clustering of evolved galaxies, starbursts, and AGNs in the key redshift range over which much of cosmic evolution has occurred; and (3) to determine the evolutionary relationship between “normal galaxies” and AGNs and the contribution of AGN accretion energy versus stellar nucleosynthesis to the cosmic backgrounds. The large area of SWIRE is important to establish statistically significant population samples over enough volume cells that we can resolve the star formation history as a function of epoch and environment, i.e., in the context of structure formation. The large volume is also optimized for finding rare objects. The SWIRE fields are likely to become the next generation of large “cosmic windows” into the extragalactic sky. They have been uniquely selected to minimize Galactic cirrus emission over large scales. The Galaxy Evolution Explorer will observe them as part of its deep 100 deg2 survey, as will Herschel. SWIRE includes ∼9 deg2 of the unique large‐area XMM Large Scale Structure hard X‐ray imaging survey and is partly covered by the UKIDSS deep J and K survey. An extensive optical/near‐IR imaging program is underway from the ground. The SWIRE data are nonproprietary; catalogs and images will be released twice yearly, beginning about 11 months after SIRTF launch. Details of the data products and release schedule are presented.

Optimal Techniques in Two‐dimensional Spectroscopy: Background Subtraction for the 21st Century

Abstract: In two‐dimensional spectrographs, the optical distortions in the spatial and dispersion directions produce variations in the subpixel sampling of the background spectrum Using knowledge of the camera distortions and the curvature of the spectral features, one can recover information regarding the background spectrum on wavelength scales much smaller than a pixel As a result, one can propagate this better sampled background spectrum through inverses of the distortion and rectification transformations and accurately model the background spectrum in two‐dimensional spectra for which the distortions have not been removed (ie, the data have not been rebinned/rectified) The procedure, as outlined in this paper, is extremely insensitive to cosmic rays, hot pixels, etc Because of this insensitivity to discrepant pixels, sky modeling and subtraction need not be performed as one of the later steps in a reduction pipeline Sky subtraction can now be performed as one of the earliest tasks, perhaps just

Classical Be Stars

Abstract: Recent results for classical Be stars are reviewed and links to general astrophysics are presented. Classical Be stars are B-type stars close to the main sequence that exhibit line emission over the photospheric spectrum. The excess is attributed to a circumstellar gaseous component that is commonly accepted to be in the form of an equatorial disk. Since 1988, when the last such review was published, major progress has been made. The geometry and kinematics of the circumstellar environment can be best explained by a rotationally supported relatively thin disk with very little outflow, consistent with interferometric observations. The presence of short-term periodic variability is restricted to the earlier type Be stars. This variation for at least some of these objects has been shown to be due to nonradial pulsation. For at least one star, evidence for a magnetic field has been observed. The mechanisms responsible for the production and dynamics of the circumstellar gas are still not constrained. Observations of nonradial pulsation beating phenomena connected to outbursts point toward a relevance of pulsation, but this mechanism cannot be generalized. Either the evidence that Be stars do not form a homogeneous group with respect to disk formation is growing or the short-term periodic variability is less important than previously thought. The statistics of Be stars investigated in open clusters of the Milky Way and the Magellanic Clouds has reopened the question of the evolutionary status of Be stars. The central B star is a fast rotator, although theoretical developments have revived the question of how high rotational rates are, so the commonly quoted mean value of about 70%-80% of the critical velocity may just be a lower limit. Be stars are in a unique position to make contributions to several important branches of stellar physics, e.g., asymmetric mass-loss processes, stellar angular momentum distribution evolution, astroseismology, and magnetic field evolution.

From molecular cores to planet-forming disks: An SIRTF legacy program

Abstract: Crucial steps in the formation of stars and planets can be studied only at mid‐ to far‐infrared wavelengths, where the Space Infrared Telescope (SIRTF) provides an unprecedented improvement in sensitivity. We will use all three SIRTF instruments (Infrared Array Camera [IRAC], Multiband Imaging Photometer for SIRTF [MIPS], and Infrared Spectrograph [IRS]) to observe sources that span the evolutionary sequence from molecular cores to protoplanetary disks, encompassing a wide range of cloud masses, stellar masses, and star‐forming environments. In addition to targeting about 150 known compact cores, we will survey with IRAC and MIPS (3.6–70 μm) the entire areas of five of the nearest large molecular clouds for new candidate protostars and substellar objects as faint as 0.001 solar luminosities. We will also observe with IRAC and MIPS about 190 systems likely to be in the early stages of planetary system formation (ages up to about 10 Myr), probing the evolution of the circumstellar dust, the raw material for planetary cores. Candidate planet‐forming disks as small as 0.1 lunar masses will be detectable. Spectroscopy with IRS of new objects found in the surveys and of a select group of known objects will add vital information on the changing chemical and physical conditions in the disks and envelopes. The resulting data products will include catalogs of thousands of previously unknown sources, multiwavelength maps of about 20 deg^2 of molecular clouds, photometry of about 190 known young stars, spectra of at least 170 sources, ancillary data from ground‐based telescopes, and new tools for analysis and modeling. These products will constitute the foundations for many follow‐up studies with ground‐based telescopes, as well as with SIRTF itself and other space missions such as SIM, JWST, Herschel, and TPF/Darwin.

The MOST Asteroseismology Mission: Ultraprecise Photometry from Space

Abstract: The Microvariablity and Oscillations of Stars (MOST) mission is a low‐cost microsatellite designed to detect low‐degree acoustic oscillations (periods of minutes) with micromagnitude precision in solar‐type stars and metal‐poor subdwarfs. There are also plans to detect light reflected from giant, short‐period, extrasolar planets and the oscillations of roAp stars and the turbulent variability in the dense winds of Wolf‐Rayet stars. This paper describes the experiment and how we met the challenge of ultraprecise photometry despite severe constraints on the mass, volume, and power available for the instrument. A side‐viewing, 150 mm aperture Rumak‐Maksutov telescope feeds two frame‐transfer CCDs, one for tracking and the other for science. There is a single 300 nm wide filter centered at 525 nm. Microlenses project Fabry images of the brighter ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage...

SN 2002cx: The Most Peculiar Known Type Ia Supernova

Abstract: We present photometric and spectroscopic observations of supernova (SN) 2002cx, which reveal it to be unique among all observed Type Ia supernovae (SNe Ia). SN 2002cx exhibits an SN 1991T–like premaximum spectrum, an SN 1991bg–like luminosity, and expansion velocities roughly half those of normal SNe Ia. Photometrically, SN 2002cx has a broad peak in the R band and a plateau phase in the I band, and slow late‐time decline. The B−V color evolution is nearly normal, but the V−R and V−I colors are very red. Early‐time spectra of SN 2002cx evolve very quickly and are dominated by lines from Fe‐group elements; features from intermediate‐mass elements (Ca, S, Si) are weak or absent. Mysterious emission lines are observed around 7000 A at about 3 weeks after maximum brightness. The nebular spectrum of SN 2002cx is also unique, consisting of narrow iron and cobalt lines. The observations of SN 2002cx are inconsistent with the observed spectral/photometric sequence and provide a major challenge to our und...

The Gemini Near‐Infrared Imager (NIRI)

Abstract: This paper presents the basic design of the Gemini Near‐Infrared Imager (NIRI) and discusses its capabilities. NIRI offers three different pixel scales to match different operating modes of the Gemini telescope and allows polarimetric and spectroscopic observations. It is equipped with an infrared on‐instrument wave‐front sensor (OIWFS) to allow tip‐tilt and focus correction even in highly obscured regions. The science detector array is an Aladdin II InSb \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} ormalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $1024\times 1024$ ...

A Globular Cluster Metallicity Scale Based on the Abundance of Fe ii

Abstract: Assuming that in the atmospheres of low-mass, metal-poor red giant stars, one-dimensional models based on local thermodynamic equilibrium accurately predict the abundance of iron from Fe ii, we derive a globular cluster metallicity scale based on the equivalent widths of Fe ii lines measured from high-resolution spectra of giants in 16 key clusters lying in the abundance range 2.4 ! (Fe/H)II ! 0.7. We base the scale largely on the analysis of spectra of 149 giant stars in 11 clusters by the Lick-Texas group supplemented by high-resolution studies of giants in five other clusters. We also derive ab initio the true distance moduli for certain key clusters (M5, M3, M13, M92, and M15) as a means of setting stellar surface gravities. Allowances are made for changes in the abundance scale if one employs (1) Kurucz models with and without convective overshooting to represent giant star atmospheres in place of MARCS models and (2) the Houdashelt et al. color-temperature scale in place of the Alonso et al. scale. We find that (Fe/H)II is correlated linearly with , the reduced strength of the near-infrared Ca ii triplet defined � W

Optical Photometry and Spectroscopy of the SN 1998bw-like Type Ic Supernova 2002ap

Abstract: We present optical photometric and spectral data of the peculiar Type Ic supernova SN 2002ap. Photometric coverage includes UBVRI bands from 2002 January 30, the day after discovery, through 2002 December 12. There are five early‐time spectra and eight in the nebular phase. We determine that SN 2002ap is similar to SN 1997ef and the gamma‐ray burst–associated SN 1998bw with respect to spectral and photometric characteristics. The nebular spectra of SN 2002ap present the largest Mg i] λ4571 to [O i] λλ6300, 6364 ratio of any supernova spectra yet published, suggesting that the progenitor of SN 2002ap was a highly stripped star. Comparing the nebular spectra of SN 1985F and SN 2002ap, we notice several similar features, casting the classification of SN 1985F as a normal Type Ib supernova in doubt. We also present nebular modeling of SN 2002ap and find that the object ejected ≳1.5 M⊙ of material within the outer velocity shell of the nebula (∼5500 km s−1) and synthesized ∼0.09 M⊙ of 56Ni.

The ROTSE‐III Robotic Telescope System

Abstract: The observation of a prompt optical flash from GRB 990123 convincingly demonstrated the value of autonomous robotic telescope systems. Pursuing a program of rapid follow-up observations of gamma- ray bursts, the Robotic Optical Transient Search Experiment (ROTSE) has developed a next-generation instrument, ROTSE-III, that will continue the search for fast optical transients. The entire system was designed as an economical robotic facility to be installed at remote sites throughout the world. There are seven major system components: optics, optical tube assembly, CCD camera, telescope mount, enclosure, environmental sensing and protection, and data acquisition. Each is described in turn in the hope that the techniques developed here will be useful in similar contexts elsewhere.

Homogeneous Photometry. III. A Star Catalog for the Open Cluster NGC 6791

Abstract: We present broadband BVI photometry for the open cluster NGC 6791, based upon analysis of 1764 individual CCD images. We discuss in detail the transformation of the instrumental magnitudes to the standard photometric system of Landolt and then discuss methods for selecting a subset of cluster stars whose photometric indices are most likely to be of high reliability. Color-magnitude and color-color diagrams for the cluster are presented and discussed. A detailed comparison of this photometry with the results of previous observational studies is presented. We make preliminary comparisons with theoretical isochrones provided by D. A. VandenBerg and conclude that an excellent match can be achieved if the metal abundance and age of the cluster are both near the upper end of the range of recent estimates ([Fe/H] ≈ +0.3, age ≈ 12 Gyr) and the reddening and true distance modulus are both near the low end of the range of recent estimates [E(B–V) ≈ 0.09 mag and (m–M)0 ≈ 12.79 mag] if the isochrone predictions are reliable. A companion paper will discuss candidate variable stars and stars possibly showing planetary transits. Data tables listing measured magnitudes and standard errors, image-quality indices, a variability index, and equinox J2000.0 equatorial coordinates for 14,342 stars to V ~ 24 have been made available to the public through the services of the Canadian Astronomy Data Centre. Equatorial coordinates only have been provided for a further 1916 stars, the photometry for which we were unable to calibrate because of lack of color information.

An Improved Distortion Solution for the Hubble Space Telescope’s WFPC21

Abstract: Having an accurate distortion correction is critical to doing accurate astrometry with the Wide Field Planetary Camera 2. Currently available solutions have serious systematic errors (∼0.2 pixel) of a skewing nature in their linear terms. We use the inner calibration field of q Centauri to find an improved cubic solution that is accurate to 0.01 pixel in the WF chips and to 0.02 pixel in the PC chip. Improvements beyond this will be difficult, as there are many factors that perturb the solution at the ∼0.01 pixel level: breathing, variations with filter, and the physical movement of the chips. There are probably not enough data available to constrain the solution to better than ∼0.01 pixel. Nevertheless, our solution is a major improvement and will allow many astrometric projects to obtain near-optimal results.

On the Progenitor of the Type II‐Plateau Supernova 2003gd in M74*

Abstract: Hubble Space Telescope (HST) WFPC2 archival F606W and F300W images obtained within 1 year prior to the explosion of the nearby Type II supernova (SN) 2003gd in M74 (=NGC 628) have been analyzed to isolate the progenitor star The SN site was located using precise astrometry applied to the HST images Two plausible candidates are identified within 0 \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} ormalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\farcs$\end{document} 6 of the SN position in the F606W image Neither candidate was detected in the F300W image SN 2003gd ap

Non‐Gaussian Error Distribution of Hubble Constant Measurements

Abstract: We construct the error distribution of Hubble constant ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} ormalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $H_{0}$ \end{document} ) measurements from Huchra’s compilation of 461 measurements of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcomm...

The Katzman Automatic Imaging Telescope Gamma-Ray Burst Alert System, and Observations of GRB 020813

Abstract: We present the technical details of the gamma-ray burst (GRB) alert system of the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory and the successful observations of the GRB 020813 optical afterglow with this system. KAIT responds to GRB alerts robotically, interrupts its prearranged program, and takes a sequence of images for each GRB alert. A grid-imaging procedure is used to increase the efficiency of the early-time observations. Different sequences of images have been developed for different types of GRB alerts. With relatively fast telescope slew and CCD readout speed, KAIT can typically complete the first observation within 60 s after receiving a GRB alert, reaching a limiting magnitude of ~19. Our reduction of the GRB 020813 data taken with KAIT shows that unfiltered magnitudes can be reliably transformed to a standard passband with a precision of ~5%, given that the color of the object is known. The GRB 020813 optical afterglow has an exceptionally slow early-time power-law decay index, although other light-curve parameters and the optical spectral index are fairly typical of GRBs.

A Primer on Eulerian Computational Fluid Dynamics for Astrophysics

Abstract: We present a pedagogical review of some of the methods employed in Eulerian computational fluid dynamics (CFD). Fluid mechanics is governed by the Euler equations, which are conservation laws for mass, momentum, and energy. The standard approach to Eulerian CFD is to divide space into finite volumes or cells and store the cell-averaged values of conserved hydro quantities. The integral Euler equations are then solved by computing the flux of the mass, momentum, and energy across cell boundaries. We review both first- order and second-order flux assignment schemes. All linear schemes are either dispersive or diffusive. The nonlinear, second-order accurate total variation diminishing (TVD) approach provides high-resolution capturing of shocks and prevents unphysical oscillations. We review the relaxing TVD scheme, a simple and robust method to solve systems of conservation laws such as the Euler equations. A three-dimensional relaxing TVD code is applied to the Sedov-Taylor blast-wave test. The propagation of the blast wave is accurately captured and the shock front is sharply resolved. We apply a three-dimensional self-gravitating hydro code to simulating the formation of blue straggler stars through stellar mergers and present some numerical results. A sample three- dimensional relaxing TVD code is provided in the Appendix.

Superhumps in Cataclysmic Binaries. XXIV. Twenty More Dwarf Novae

Abstract: We report precise measures of the orbital and superhump period in 20 more dwarf novae. For 10 stars, we report new and confirmed spectroscopic periods—signifying the orbital period —as well as the P o

A search for core-collapse supernova progenitors in Hubble Space Telescope images

Abstract: Identifying the massive progenitor stars that give rise to core‐collapse supernovae (SNe) is one of the main pursuits of supernova and stellar evolution studies. Using ground‐based images of recent, nearby SNe obtained primarily with the Katzman Automatic Imaging Telescope, astrometry from the Two Micron All Sky Survey, and archival images from the Hubble Space Telescope, we have attempted the direct identification of the progenitors of 16 Type II and Type Ib/c SNe. We may have identified the progenitors of the Type II SNe 1999br in NGC 4900, 1999ev in NGC 4274, and 2001du in NGC 1365 as supergiant stars with \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} o...

Molecular Hydrogen Optical Depth Templates for FUSE Data Analysis

Abstract: The calculation and use of molecular hydrogen optical depth templates to quickly identify and model molecular hydrogen absorption features longward of the Lyman edge at 912 Angstroms are described. Such features are commonly encountered in spectra obtained by the Far Ultraviolet Spectroscopic Explorer and also in spectra obtained by the Space Telescope Imaging Spectrograph, albeit less commonly. Individual templates are calculated containing all the Lyman and Werner transitions originating from a single rotational state (J'') of the 0th vibrational level (v'') of the ground electronic state. Templates are provided with 0.01 Angstrom sampling for doppler parameters ranging from 2 <= b <= 20 km s^-1 and rotational states 0 <= J'' <= 15. Optical depth templates for excited vibrational states are also available for select doppler parameters. Each template is calculated for a fiducial column density of log[N(cm^-2)] = 21 and may be scaled to any column less than this value without loss of accuracy. These templates will facilitate the determination of the distribution of molecular hydrogen column density as a function of rotational level. The use of these templates will free the user from the computationally intensive task of calculating profiles for a large number of lines and allow concentration on line profile or curve-of-growth fitting to determine column densities and doppler parameters. The templates may be downloaded freely from http://www.pha.jhu.edu/~stephan/h2ools2.html

Optical and infrared photometry of the unusual Type Ia supernova 2000cx

Abstract: We present optical and infrared photometry of the unusual Type Ia supernova 2000cx. With the data of Li et al. and Jha, this constitutes the largest data set ever assembled for a Type Ia SN, more than 600 points in UBVRIJHK. We confirm the finding of Li et al. regarding the unusually blue B−V colors as SN 2000cx entered the nebular phase. Its I‐band secondary hump was extremely weak given its B‐band decline rate. The V minus near‐infrared colors likewise do not match loci based on other slowly declining Type Ia SNe, although V−K is the least “abnormal.” In several ways, SN 2000cx resembles other slow decliners, given its B‐band decline rate [ \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \ren...

Comparing Deep Mixing in Globular Cluster and Halo Field Giants: Carbon Abundance Data from the Literature

Abstract: The behavior of carbon abundance as a function of luminosity is used to compare the rates of deep mixing within red giants of four globular clusters and the Galactic halo field population. Measurements of [C/Fe] for the clusters M92, NGC 6397, M3, and M13 have been compiled from the literature, together with the Gratton et al. data for halo field stars. Plots of [C/Fe] versus absolute visual magnitude show that for MV < +1.6 the rate of decline of carbon abundance with increasing luminosity on the red giant branch is d[C/Fe]/dMV ≈ 0.22 ± 0.03 among the field stars, as well as in M92, NGC 6397, and M3. Among giants fainter than MV = +1.6 the variation of [C/Fe] with absolute magnitude is much less. The data indicate that the rate at which deep mixing introduces carbon-depleted material into the convective envelopes of field halo stars during the upper red giant branch phase of evolution is similar to that of many globular cluster giants. The notable exception appears to be M13, in which stars exhibit deep mixing at a greater rate; this may account for the high incidence of very low oxygen abundances among the most luminous giants in M13 in comparison to M3.

An Externally Dispersed Interferometer Prototype for Sensitive Radial Velocimetry: Theory and Demonstration on Sunlight

Abstract: A theory of operation of a wideband interferometric Doppler spectroscopy technique, called externally dispersed interferometry (EDI), is presented. The first EDI prototype was tested on sunlight and detected the 12 m s 1 amplitude lunar signature in Earth's motion. The hybrid instrument is an undispersed Michelson interferometer having a fixed delay of about 1 cm, in series with an external spectrograph of about 20,000 resolution. The Michelson provides the Doppler shift discrimination, while the external spectrograph boosts net white-light fringe visibility by reducing cross talk from adjacent continuum channels. A moireeffect between the sinusoidal interferometer transmission and the input spectrum heterodynes high spectral details to broad moire ´ patterns, which carry the Doppler information in its phase. These broad patterns survive the blurring of the spectrograph, which can have several times lower resolution than grating-only spectrographs typically used now for the Doppler planet search. This enables the net instrument to be dramatically smaller in size (∼1 m) and cost. The EDI behavior is compared and contrasted to the conventional grating-only technique.

Dynamical Stability of Earth-like Planetary Orbits in Binary Systems

Abstract: This paper explores the stability of an Earth-like planet orbiting a solar-mass star in the presence of an outer-lying intermediate-mass companion. The overall goal is to estimate the fraction of binary systems that allow Earth-like planets to remain stable over long timescales. We numerically determine the planet's ejection time tej over a range of companion masses ( ), orbital eccentricities e, and semimajor axes M p 0.001-0.5 M C , a. This suite of ∼40,000 numerical experiments suggests that the most important variables are the companion's mass and periastron distance to the primary star. At fixed , the ejection time is a steeply MR p a(1 e) M C min C increasing function of over the range of parameter space considered here (although the ejection time has a Rmin distribution of values for a given ). Most of the integration times are limited to 10 Myr, but a small set of Rmin integrations extend to 500 Myr. For each companion mass, we find fitting formulae that approximate the mean ejection time as a function of . These functions can then be extrapolated to longer timescales. By combining Rmin the numerically determined ejection times with the observed distributions of orbital parameters for binary systems, we estimate that (at least) 50% of binaries allow an Earth-like planet to remain stable over the 4.6 Gyr age of our solar system.

Astrophysics in 2002

Abstract: This has been the Year of the Baryon. Some low temperature ones were seen at high redshift, some high temperature ones were seen at low redshift, and some cooling ones were (probably) reheated. Astronomers saw the back of the Sun (which is also made of baryons), a possible solution to the problem of ejection of material by Type II Supernovae (in which neutrinos push out baryons), the production of R Coronae Borealis stars (previously-owned baryons), and perhaps found the missing satellite galaxies (whose failing is that they have no baryons). A few questions were left unanswered for next year, and an attempt is made to discuss these as well.

Median Statistics and the Mass Density of the Universe

Abstract: We use weighted mean and median statistics techniques to combine individual estimates of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} ewcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} ormalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\Omega _{M,0}$ \end{document} , the present mean mass density in nonrelativistic matter, and determine the observed values and ranges of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usep...