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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Parallaxes of southern extremely cool objects (parsec). II. Spectroscopic follow-up and parallaxes of 52 targets

We present near-infrared spectroscopy for 52 ultracool dwarfs, including two newly discovered late-M dwarfs, one new late-M subdwarf candidate, three new L, and four new T dwarfs. We also present parallaxes and proper motions for 21 of them. Four of the targets presented here have previous parallax measurements, while all the others are new values. This allow us to populate further the spectral sequence at early types (L0-L4). Combining the astrometric parameters with the new near-infrared spectroscopy presented here, we are able to investigate further the nature of some of the objects. In particular, we find that the peculiar blue L1 dwarf SDSS J133148.92–011651.4 is a metal-poor object, likely a member of the galactic thick disk. We discover a new M subdwarf candidate, 2MASS J20115649–6201127. We confirm the low-gravity nature of EROS-MP J0032–4405, DENIS-P J035726.9–441730, and 2MASS J22134491–2136079. We present two new metal-poor dwarfs: the L4pec 2MASS J19285196–4356256 and the M7pec SIPS2346–5928. We also determine the effective temperature and bolometric luminosity of the 21 targets with astrometric measurements, and we obtain a new polynomial relation between effective temperature and near-infrared spectral type. The new fit suggests a flattening of the sequence at the transition between M and L spectral types. This could be an effect of dust formation, which causes a more rapid evolution of the spectral features as a function of the effective temperature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

CCD Photometry of bright stars using objective wire mesh

Obtaining accurate photometry of bright stars from the ground remains problematic due to the danger of overexposing the target and/or the lack of suitable nearby comparison stars. The century-old method of using objective wire mesh to produce multiple stellar images seems promising for the precise CCD photometry of such stars. Furthermore, our tests on β Cep and its comparison star, differing by 5 mag, are very encouraging. Using a CCD camera and a 20 cm telescope with the objective covered by a plastic wire mesh, in poor weather conditions, we obtained differential photometry with a precision of 4.5 mmag per two minute exposure. Our technique is flexible and may be tuned to cover a range as big as 6-8 mag. We discuss the possibility of installing a wire mesh directly in the filter wheel.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A technique to derive improved proper motions for Kepler objects of interest

We outline an approach yielding proper motions with higher precision than exists in present catalogs for a sample of stars in the Kepler field. To increase proper-motion precision, we combine first-moment centroids of Kepler pixel data from a single season with existing catalog positions and proper motions. We use this astrometry to produce improved reduced-proper-motion diagrams, analogous to a Hertzsprung-Russell (H-R) diagram, for stars identified as Kepler objects of interest. The more precise the relative proper motions, the better the discrimination between stellar luminosity classes. Using UCAC4 and PPMXL epoch 2000 positions (and proper motions from those catalogs as quasi-Bayesian priors), astrometry for a single test Channel (21) and Season (0) spanning 2 yr yields proper motions with an average per-coordinate proper-motion error of 1.0 mas yr{sup –1}, which is over a factor of three better than existing catalogs. We apply a mapping between a reduced-proper-motion diagram and an H-R diagram, both constructed using Hubble Space Telescope parallaxes and proper motions, to estimate Kepler object of interest K-band absolute magnitudes. The techniques discussed apply to any future small-field astrometry as well as to the rest of the Kepler field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

YSOVAR: MID-INFRARED VARIABILITY OF YOUNG STELLAR OBJECTS AND THEIR DISKS IN THE CLUSTER IRAS 20050+2720

We present a time-variability study of young stellar objects (YSOs) in the cluster IRAS 20050+2720, performed at 3.6 and 4.5 μm with the Spitzer Space Telescope; this study is part of the Young Stellar Object VARiability (YSOVAR) project. We have collected light curves for 181 cluster members over 60 days. We find a high variability fraction among embedded cluster members of ca. 70%, whereas young stars without a detectable disk display variability less often (in ca. 50% of the cases) and with lower amplitudes. We detect periodic variability for 33 sources with periods primarily in the range of 2–6 days. Practically all embedded periodic sources display additional variability on top of their periodicity. Furthermore, we analyze the slopes of the tracks that our sources span in the color–magnitude diagram (CMD). We find that sources with long variability time scales tend to display CMD slopes that are at least partially influenced by accretion processes, while sources with short variability timescales tend to display extinction-dominated slopes. We find a tentative trend of X-ray detected cluster members to vary on longer timescales than the X-ray undetected members.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

DYNAMICALLY EXCITED OUTER SOLAR SYSTEM OBJECTS IN THE HUBBLE SPACE TELESCOPE ARCHIVE

We present the faintest mid-ecliptic latitude survey in the second part of Hubble Space Telescope archival search for outer solar system bodies. We report the discovery of 28 new trans-Neptunian objects and one small centaur (R {approx} 2 km) in the band 5 Degree-Sign -20 Degree-Sign off the ecliptic. The inclination distribution of these excited objects is consistent with the distribution derived from brighter ecliptic surveys. We suggest that the size and inclination distribution should be estimated consistently using suitable surveys with calibrated search algorithms and reliable orbital information.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

DEEP VERY LARGE ARRAY RADIO CONTINUUM SURVEYS OF GLIMPSE EXTENDED GREEN OBJECTS (EGOs)

We present the results of deep, high angular resolution Very Large Array surveys for radio continuum emission toward a sample of 14 GLIMPSE Extended Green Objects (EGOs). Identified as massive young stellar object (MYSO) outflow candidates based on their extended 4.5 {mu}m emission in Spitzer images, the EGOs in our survey sample are also associated with 6.7 GHz Class II and/or 44 GHz Class I CH{sub 3}OH masers. No continuum is detected at 3.6 or 1.3 cm toward the majority (57%) of our targets (median rms {approx}0.03 and 0.25 mJy beam{sup -1}). Only two EGOs are associated with optically thin emission consistent with ultracompact/compact H II regions. Both of these sources exhibit cm-{lambda} multiplicity, with evidence that one of the less-evolved members may be driving the 4.5 {mu}m outflow. Most of the other cm-{lambda} EGO counterparts are weak ({approx}<1 mJy), unresolved, undetected at 1.3 cm, and characterized by intermediate spectral indices consistent with hypercompact (HC) H II regions or ionized winds or jets. One EGO centimeter (cm) counterpart, likely an optically thick HC H II region, is detected only at 1.3 cm and is associated with hot core line emission and H{sub 2}O and 6.7 GHz CH{sub 3}OH masers. The results of our exceptionally sensitive survey indicate that EGOs signify an early stage of massive star formation, before photoionizing feedback from the central MYSO significantly influences the (proto)cluster environment. Actively driving outflows (and so, presumably, actively accreting), the surveyed EGOs are associated with significant clump-scale gas reservoirs, providing sufficient material for sustained, rapid accretion.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

NEOWISE OBSERVATIONS OF NEAR-EARTH OBJECTS: PRELIMINARY RESULTS

With the NEOWISE portion of the Wide-field Infrared Survey Explorer (WISE) project, we have carried out a highly uniform survey of the near-Earth object (NEO) population at thermal infrared wavelengths ranging from 3 to 22 {mu}m, allowing us to refine estimates of their numbers, sizes, and albedos. The NEOWISE survey detected NEOs the same way whether they were previously known or not, subject to the availability of ground-based follow-up observations, resulting in the discovery of more than 130 new NEOs. The survey's uniform sensitivity, observing cadence, and image quality have permitted extrapolation of the 428 near-Earth asteroids (NEAs) detected by NEOWISE during the fully cryogenic portion of the WISE mission to the larger population. We find that there are 981 {+-} 19 NEAs larger than 1 km and 20,500 {+-} 3000 NEAs larger than 100 m. We show that the Spaceguard goal of detecting 90% of all 1 km NEAs has been met, and that the cumulative size distribution is best represented by a broken power law with a slope of 1.32 {+-} 0.14 below 1.5 km. This power-law slope produces {approx}13, 200 {+-} 1900 NEAs with D > 140 m. Although previous studies predict another break in the cumulative size distribution below D {approx} 50-100 m, resulting in an increase in the number of NEOs in this size range and smaller, we did not detect enough objects to comment on this increase. The overall number for the NEA population between 100 and 1000 m is lower than previous estimates. The numbers of near-Earth comets and potentially hazardous NEOs will be the subject of future work.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

FIRST KECK NULLING OBSERVATIONS OF A YOUNG STELLAR OBJECT: PROBING THE CIRCUMSTELLAR ENVIRONMENT OF THE HERBIG Ae STAR MWC 325

We present the first N-band nulling plus K- and L-band V{sup 2} observations of a young stellar object, MWC 325, taken with the 85 m baseline Keck Interferometer. The Keck nuller was designed for the study of faint dust signatures associated with debris disks, but it also has a unique capability for studying the temperature and density distribution of denser disks found around young stellar objects. Interferometric observations of MWC 325 at K, L, and N encompass a factor of five in spectral range and thus, especially when spectrally dispersed within each band, enable characterization of the structure of the inner disk regions where planets form. Fitting our observations with geometric models such as a uniform disk or a Gaussian disk show that the apparent size increases monotonically with wavelength in the 2-12 {mu}m wavelength region, confirming the widely held assumption based on radiative transfer models, now with spatially resolved measurements over a broad wavelength range, that disks are extended with a temperature gradient. The effective size is a factor of about 1.4 and 2.2 larger in the L band and N band, respectively, compared to that in the K band. The existing interferometric measurements and the spectral energy distribution can be reproduced by a flat disk or a weakly shadowed nearly flat disk model, with only slight flaring in the outer regions of the disk, consisting of representative 'sub-micron' (0.1 {mu}m) and 'micron' (2 {mu}m) grains of a 50:50 ratio of silicate and graphite. This is in marked contrast to the disks previously found in other Herbig Ae/Be stars, suggesting a wide variety in the disk properties among Herbig Ae/Be stars.

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DOE OSTI2012

A HIGHLY COLLIMATED WATER MASER BIPOLAR OUTFLOW IN THE CEPHEUS A HW3d MASSIVE YOUNG STELLAR OBJECT

We present the results of multi-epoch very long baseline interferometry (VLBI) water (H{sub 2}O) maser observations carried out with the VLBI Exploration of Radio Astrometry toward the Cepheus A HW3d object. We measured for the first time relative proper motions of the H{sub 2}O maser features, whose spatio-kinematics traces a compact bipolar outflow. This outflow looks highly collimated and expanding through {approx}280 AU (400 mas) at a mean velocity of {approx}21 km s{sup -1} ({approx}6 mas yr{sup -1}) without taking into account the turbulent central maser cluster. The opening angle of the outflow is estimated to be {approx}30 Degree-Sign . The dynamical timescale of the outflow is estimated to be {approx}100 years. Our results provide strong support that HW3d harbors an internal massive young star, and the observed outflow could be tracing a very early phase of star formation. We also have analyzed Very Large Array archive data of 1.3 cm continuum emission obtained in 1995 and 2006 toward Cepheus A. The comparative result of the HW3d continuum emission suggests the possibility of the existence of distinct young stellar objects in HW3d and/or strong variability in one of their radio continuum emission components.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

CHARACTERIZATION OF ACTIVE MAIN BELT OBJECT P/2012 F5 (GIBBS): A POSSIBLE IMPACTED ASTEROID

In this work, we characterize the recently discovered active main belt object P/2012 F5 (Gibbs), which was discovered with a dust trail >7' in length in the outer main belt, 7 months prior to aphelion. We use optical imaging obtained on UT 2012 March 27 to analyze the central condensation and the long trail. We find B-band and R-band apparent magnitudes of 20.96 {+-} 0.04 mag and 19.93 {+-} 0.02 mag, respectively, which give an upper limit on the radius of the nucleus of 2.1 km. The geometric scattering cross-section of material in the trail was {approx}4 Multiplication-Sign 10{sup 8} m{sup 2}, corresponding to a mass of {approx}5 Multiplication-Sign 10{sup 7} kg. Analysis of infrared images taken by the Wide-field Infrared Survey Explorer in 2010 September reveals that the object was below the detection limit, suggesting that it was less active than it was during 2012, or possibly inactive, just six months after it passed through perihelion. We set a 1{sigma} upper limit on its radius during this time of 2.9 km. P/2012 F5 (Gibbs) is dynamically stable in the outer main belt on timescales of {approx}1 Gyr, pointing toward an asteroidal origin. We find that the morphology of the ejected dust is consistent with it being produced by a single event that occurred on UT 2011 July 7 {+-} 20 days, possibly as the result of a collision with a small impactor.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

MEASURING THE ABUNDANCE OF SUB-KILOMETER-SIZED KUIPER BELT OBJECTS USING STELLAR OCCULTATIONS

We present here the analysis of about 19,500 new star hours of low ecliptic latitude observations (|b| {<=} 20 Degree-Sign ) obtained by the Hubble Space Telescope's Fine Guidance Sensors over a time span of more than nine years, which is in addition to the {approx}12, 000 star hours previously analyzed by Schlichting et al. Our search for stellar occultations by small Kuiper Belt Objects (KBOs) yielded one new candidate event corresponding to a body with a 530 {+-} 70 m radius at a distance of about 40 AU. Using bootstrap simulations, we estimate a probability of Almost-Equal-To 5% that this event is due to random statistical fluctuations within the new data set. Combining this new event with the single KBO occultation reported by Schlichting et al. we arrive at the following results: (1) the ecliptic latitudes of 6. Degree-Sign 6 and 14. Degree-Sign 4 of the two events are consistent with the observed inclination distribution of larger, 100-km-sized KBOs. (2) Assuming that small, sub-kilometer-sized KBOs have the same ecliptic latitude distribution as their larger counterparts, we find an ecliptic surface density of KBOs with radii larger than 250 m of N(r > 250 m) = 1.1{sup +1.5}{sub -0.7} Multiplication-Sign 10{sup 7} deg{sup -2}; if sub-kilometer-sized KBOs have instead a uniform ecliptic latitude distribution for -20 Degree-Sign < b < 20 Degree-Sign then N(r > 250 m) = 4.4{sup +5.8}{sub -2.8} Multiplication-Sign 10{sup 6} deg{sup -2}. This is the best measurement of the surface density of sub-kilometer-sized KBOs to date. (3) Assuming the KBO size distribution can be well described by a single power law given by N(> r){proportional_to}r{sup 1-q}, where N(> r) is the number of KBOs with radii greater than r, and q is the power-law index, we find q = 3.8 {+-} 0.2 and q = 3.6 {+-} 0.2 for a KBO ecliptic latitude distribution that follows the observed distribution for larger, 100-km-sized KBOs and a uniform KBO ecliptic latitude distribution for -20 Degree-Sign < b < 20 Degree-Sign , respectively. (4) Regardless of the exact power law, our results suggest that small KBOs are numerous enough to satisfy the required supply rate for the Jupiter family comets. (5) We can rule out a single power law below the break with q > 4.0 at 2{sigma}, confirming a strong deficit of sub-kilometer-sized KBOs compared to a population extrapolated from objects with r > 45 km. This suggests that small KBOs are undergoing collisional erosion and that the Kuiper Belt is a true analog to the dust producing debris disks observed around other stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

VARIABILITY AT THE EDGE: OPTICAL NEAR/IR RAPID-CADENCE MONITORING OF NEWLY OUTBURSTING FU ORIONIS OBJECT HBC 722

We present the detection of day-timescale periodic variability in the r-band lightcurve of newly outbursting FU Orionis-type object HBC 722, taken from >42 nights of observation with the CQUEAN instrument on the McDonald Observatory 2.1 m telescope. The optical/near-IR lightcurve of HBC 722 shows a complex array of periodic variability, clustering around 5.8-day (0.044 mag amplitude) and 1.28-day (0.016 mag amplitude) periods, after removal of overall baseline variation. We attribute the unusual number of comparable strength signals to a phenomenon related to the temporary increase in accretion rate associated with FUors. We consider semi-random 'flickering', magnetic braking/field compression and rotational asymmetries in the disk instability region as potential sources of variability. Assuming that the 5.8-day period is due to stellar rotation and the 1.28-day period is indicative of Keplerian rotation at the inner radius of the accretion disk (at 2 R {sub *}), we derive a B-field strength of 2.2-2.7 kG, slightly larger than typical T Tauri stars. If instead the 5.8-day signal is from a disk asymmetry, the instability region has an outer radius of 5.4 R {sub *}, consistent with models of FUor disks. Further exploration of the time domain in this complicated source and related objects will be key to understanding accretion processes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

A WATER MASER AND NH{sub 3} SURVEY OF GLIMPSE EXTENDED GREEN OBJECTS

We present the results of a Nobeyama 45 m H{sub 2}O maser and NH{sub 3} survey of all 94 northern GLIMPSE extended green objects (EGOs), a sample of massive young stellar objects (MYSOs) identified based on their extended 4.5 {mu}m emission. We observed the NH{sub 3}(1,1), (2,2), and (3,3) inversion lines, and detected emission toward 97%, 63%, and 46% of our sample, respectively (median rms {approx} 50 mK). The H{sub 2}O maser detection rate is 68% (median rms {approx} 0.11 Jy). The derived H{sub 2}O maser and clump-scale gas properties are consistent with the identification of EGOs as young MYSOs. To explore the degree of variation among EGOs, we analyze subsamples defined based on mid-infrared (MIR) properties or maser associations. H{sub 2}O masers and warm dense gas, as indicated by emission in the higher-excitation NH{sub 3} transitions, are most frequently detected toward EGOs also associated with both Class I and II CH{sub 3}OH masers. Ninety-five percent (81%) of such EGOs are detected in H{sub 2}O (NH{sub 3}(3,3)), compared to only 33% (7%) of EGOs without either CH{sub 3}OH maser type. As populations, EGOs associated with Class I and/or II CH{sub 3}OH masers have significantly higher NH{sub 3} line widths, column densities, and kinetic temperatures than EGOs undetected in CH{sub 3}OH maser surveys. However, we find no evidence for statistically significant differences in H{sub 2}O maser properties (such as maser luminosity) among any EGO subsamples. Combining our data with the 1.1 mm continuum Bolocam Galactic Plane Survey, we find no correlation between isotropic H{sub 2}O maser luminosity and clump number density. H{sub 2}O maser luminosity is weakly correlated with clump (gas) temperature and clump mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE PRISM MULTI-OBJECT SURVEY (PRIMUS). II. DATA REDUCTION AND REDSHIFT FITTING

The PRIsm MUlti-object Survey (PRIMUS) is a spectroscopic galaxy redshift survey to z {approx} 1 completed with a low-dispersion prism and slitmasks allowing for simultaneous observations of {approx}2500 objects over 0.18 deg{sup 2}. The final PRIMUS catalog includes {approx}130,000 robust redshifts over 9.1 deg{sup 2}. In this paper, we summarize the PRIMUS observational strategy and present the data reduction details used to measure redshifts, redshift precision, and survey completeness. The survey motivation, observational techniques, fields, target selection, slitmask design, and observations are presented in Coil et al. Comparisons to existing higher-resolution spectroscopic measurements show a typical precision of {sigma}{sub z}/(1 + z) = 0.005. PRIMUS, both in area and number of redshifts, is the largest faint galaxy redshift survey completed to date and is allowing for precise measurements of the relationship between active galactic nuclei and their hosts, the effects of environment on galaxy evolution, and the build up of galactic systems over the latter half of cosmic history.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DETECTION OF COMA ACTIVITY OF THE ACO/QUASI-HILDA OBJECT 212P/2000YN{sub 30}

The quasi-Hilda object 212P/2000YN{sub 30}, which has a cometary-like orbit, was found to display a dust tail structure between 2009 January and March. From orbital calculations, it is shown that this object could have been an active comet in the past before being transported to its current orbital configuration in quasi-stable 3:2 resonance with Jupiter.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

AN ANALYSIS OF THE ENVIRONMENTS OF FU ORIONIS OBJECTS WITH HERSCHEL

We present Herschel-HIFI, SPIRE, and PACS 50-670 {mu}m imaging and spectroscopy of six FU Orionis-type objects and candidates (FU Orionis, V1735 Cyg, V1515 Cyg, V1057 Cyg, V1331 Cyg, and HBC 722), ranging in outburst date from 1936 to 2010, from the 'FOOSH' (FU Orionis Objects Surveyed with Herschel) program, as well as ancillary results from Spitzer Infrared Spectrograph and the Caltech Submillimeter Observatory. In their system properties (L{sub bol}, T{sub bol}, and line emission), we find that FUors are in a variety of evolutionary states. Additionally, some FUors have features of both Class I and II sources: warm continuum consistent with Class II sources, but rotational line emission typical of Class I, far higher than Class II sources of similar mass/luminosity. Combining several classification techniques, we find an evolutionary sequence consistent with previous mid-IR indicators. We detect [O I] in every source at luminosities consistent with Class 0/I protostars, much greater than in Class II disks. We detect transitions of {sup 13}CO (J{sub up} of 5-8) around two sources (V1735 Cyg and HBC 722) but attribute them to nearby protostars. Of the remaining sources, three (FU Ori, V1515 Cyg, and V1331 Cyg) exhibit only low-lying CO, but one (V1057 Cyg) shows CO up to J = 23 {yields} 22 and evidence for H{sub 2}O and OH emission, at strengths typical of protostars rather than T Tauri stars. Rotational temperatures for 'cool' CO components range from 20 to 81 K, for {approx} 10{sup 50} total CO molecules. We detect [C I] and [N II] primarily as diffuse emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

DIRECT IMAGING OF A COMPACT MOLECULAR OUTFLOW FROM A VERY LOW LUMINOSITY OBJECT: L1521F-IRS

Studying the physical conditions of very low luminosity objects (VeLLOs; L{sub bol} < 0.1 L{sub Sun }) is important for understanding the earliest evolutionary stage of protostars and brown dwarfs. We report interferometric observations of the VeLLO L1521F-IRS, in {sup 12}CO (2-1) line emission and the 1.3 mm continuum emission, using the Submillimeter Array. With the {sup 12}CO (2-1) high-resolution observations, we have spatially resolved a compact but poorly collimated molecular outflow associated with L1521F-IRS for the first time. The blueshifted and redshifted lobes are aligned along the east and west side of L1521F-IRS with a lobe size of Almost-Equal-To 1000 AU. The estimated outflow mass, maximum outflow velocity, and outflow force are (9.0-80) Multiplication-Sign 10{sup -4} M{sub Sun }, 7.2 km s{sup -1}, and (7.4-66) Multiplication-Sign 10{sup -7} M{sub Sun} km s{sup -1} yr{sup -1}, respectively. The estimated outflow parameters such as size, mass, and momentum rate are similar to values derived for other VeLLOs, and are located at the lower end of values compared to previously studied outflows associated with low- to high-mass star-forming regions. Low-velocity less collimated (1.5 km s{sup -1}/1200 AU) and higher-velocity compact (4.0 km s{sup -1}/920 AU) outflow components are suggested by the data. These velocity structures are not consistent with those expected in the jet-driven or wind-driven outflow models, perhaps suggesting a remnant outflow from the first hydrostatic core as well as an undeveloped outflow from the protostar. Detection of an infrared source and compact millimeter continuum emission suggests the presence of the protostar, while its low bolometric luminosity (0.034-0.07 L{sub Sun }) and small outflow suggests that L1521F is in the earliest protostellar stage (<10{sup 4} yr) and contains a substellar mass object. The bolometric (or internal) luminosity of L1521F-IRS suggests that the current mass accretion rate is an order of magnitude lower than expected in the standard mass accretion model ( Almost-Equal-To 10{sup -6} M{sub Sun} yr{sup -1}), which may imply that L1521F-IRS is currently in a low activity phase.

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DOE OSTI2013

THE LOCATIONS OF SHORT GAMMA-RAY BURSTS AS EVIDENCE FOR COMPACT OBJECT BINARY PROGENITORS

We present a detailed investigation of Hubble Space Telescope rest-frame UV/optical observations of 22 short gamma-ray burst (GRB) host galaxies and sub-galactic environments. Utilizing the high angular resolution and depth of HST we characterize the host galaxy morphologies, measure precise projected physical and host-normalized offsets between the bursts and host centers, and calculate the locations of the bursts with respect to their host light distributions (rest-frame UV and optical). We calculate a median short GRB projected physical offset of 4.5 kpc, about 3.5 times larger than that for long GRBs, and find that ≈25% of short GRBs have offsets of ∼> 10 kpc. When compared to their host sizes, the median offset is 1.5 half-light radii (r{sub e} ), about 1.5 times larger than the values for long GRBs, core-collapse supernovae, and Type Ia supernovae. In addition, ≈20% of short GRBs having offsets of ∼> 5r{sub e} , and only ≈25% are located within 1r{sub e} . We further find that short GRBs severely under-represent their hosts' rest-frame optical and UV light, with ≈30%-45% of the bursts located in regions of their host galaxies that have no detectable stellar light, and ≈55% in the regions with no UV light. Therefore, short GRBs do not occur in regions of star formation or even stellar mass. This demonstrates that the progenitor systems of short GRBs must migrate from their birth sites to their eventual explosion sites, a signature of kicks in compact object binary systems. Utilizing the full sample of offsets, we estimate natal kick velocities of ≈20-140 km s{sup –1}. These independent lines of evidence provide the strongest support to date that short GRBs result from the merger of compact object binaries (NS-NS/NS-BH)

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