Smithsonian Astrophysical Observatory

About: Smithsonian Astrophysical Observatory is a facility organization based out in Cambridge, Massachusetts, United States. It is known for research contribution in the topics: Galaxy & Stars. The organization has 1665 authors who have published 3622 publications receiving 132183 citations. The organization is also known as: SAO.

OPTICAL SPECTROSCOPIC OBSERVATIONS OF BLAZARS AND γ-RAY BLAZAR CANDIDATES IN THE SLOAN DIGITAL SKY SURVEY DATA RELEASE NINE

Abstract: We present an analysis of the optical spectra available in the Sloan Digital Sky Survey data release nine (SDSS DR9) for the blazars listed in the ROMA-BZCAT and for the γ-ray blazar candidates selected according to their IR colors. First, we adopt a statistical approach based on Monte Carlo simulations to find the optical counterparts of the blazars listed in the ROMA-BZCAT catalog. Then, we crossmatched the SDSS spectroscopic catalog with our selected samples of blazars and γ-ray blazar candidates, searching for those with optical spectra available to classify our blazar-like sources and, whenever possible, to confirm their redshifts. Our main objectives are to determine the classification of uncertain blazars listed in the ROMA-BZCAT and to discover new gamma-ray blazars. For the ROMA-BZCAT sources, we investigated a sample of 84 blazars, confirming the classification for 20 of them and obtaining 18 new redshift estimates. For the γ-ray blazars, indicated as potential counterparts of unassociated Fermi sources or with uncertain nature, we established the blazar-like nature of 8 out of the 27 sources analyzed and confirmed 14 classifications.

Protostars in the Elephant Trunk Nebula

Abstract: The optically dark globule IC 1396A is revealed using Spitzer Space Telescope images at 3.6, 4.5, 5.8, 8, and 24 μm to be infrared-bright and to contain a set of previously unknown protostars. The mid-infrared colors of the 24 μm detected sources indicate several very young (Class I or 0) protostars and a dozen Class II stars. Three of the new sources (IC 1396A:γ, 1396A:δ, and 1396A:) emit over 90% of their bolometric luminosities at wavelengths greater than 3 μm, and they are located within ~0.02 pc of the ionization front at the edge of the globule. Many of the sources have spectra that are still rising at 24 μm. The two previously known young stars LkHα 349a and 349c are both detected, with component c harboring a massive disk and component a being bare. On the order of 5% of the mass of material in the globule is presently in the form of protostars in the 105-106 yr age range. This high star formation rate was likely triggered by radiation from a nearby O star.

The Herbig Ae Star HD 163296 in X-Rays

Abstract: Chandra X-ray imaging spectroscopy of the nearby Herbig Ae star HD 163296 at 100 AU angular resolution is reported. A point-like, soft (kT approximately 0.5 approximately kev), emission-line source is detected at the location of the star with an X-ray luminosity of 4.0e29 erg/s. In addition, faint emission along the direction of a previously-detected Ly-alpha-emitting jet and Herbig-Haro outflow may be present. The relatively low luminosity, lack of a hard spectral component, and absence of strong X-ray variability in HD 163296 can be explained as originating from optically-thin shock-heated gas accreting onto the stellar surface along magnetic field lines. This would require a (dipole) magnetic field strength at the surface of HD 163296 of at least approximately 100 approximately G and perhaps as high as several kG.

The Fornax Deep Survey with the VST. IV. A size and magnitude limited catalog of dwarf galaxies in the area of the Fornax cluster

Abstract: Context. The Fornax Deep Survey (FDS), an imaging survey in the u', g', r', and i'-bands, has a supreme resolution and image depth compared to the previous spatially complete Fornax Cluster Catalog (FCC). Our new data allows us to study the galaxies down to r'-band magnitude m(r') approximate to 21 mag (M-r' approximate to -10.5 mag), which opens a new parameter regime to investigate the evolution of dwarf galaxies in the cluster environment. After the Virgo cluster, Fornax is the second nearest galaxy cluster to us, and with its different mass and evolutionary state, it provides a valuable comparison that makes it possible to understand the various evolutionary effects on galaxies and galaxy clusters. These data provide an important legacy dataset to study the Fornax cluster. Aims. We aim to present the Fornax Deep Survey (FDS) dwarf galaxy catalog, focusing on explaining the data reduction and calibrations, assessing the quality of the data, and describing the methods used for defining the cluster memberships and first order morphological classifications for the catalog objects. We also describe the main scientific questions that will be addressed based on the catalog. This catalog will also be invaluable for future follow-up studies of the Fornax cluster dwarf galaxies. Methods. As a first step we used the SExtractor fine-tuned for dwarf galaxy detection, to find galaxies from the FDS data, covering a 26 deg(2) area of the main cluster up to its virial radius, and the area around the Fornax A substructure. We made 2D-decompositions of the identified galaxies using GALFIT, measure the aperture colors, and the basic morphological parameters like concentration and residual flux fraction. We used color-magnitude, luminosity-radius and luminosity-concentration relations to separate the cluster galaxies from the background galaxies. We then divided the cluster galaxies into early- and late-type galaxies according to their morphology and gave first order morphological classifications using a combination of visual and parametric classifications. Results. Our final catalog includes 14 095 galaxies. We classify 590 galaxies as being likely Fornax cluster galaxies, of which 564 are dwarfs (M-r' (') > -18.5 mag) consisting our Fornax dwarf catalog. Of the cluster dwarfs we classify 470 as early-types, and 94 as late-type galaxies. Our final catalog reaches its 50% completeness limit at magnitude M-r' = -10.5 mag and surface brightness (mu) over bar (e,r') = 26 mag arcsec(-2), which is approximately three magnitudes deeper than the FCC. Based on previous works and comparison with a spectroscopically confirmed subsample, we estimate that our final Fornax dwarf galaxy catalog has less than or similar to 10% contamination from the background objects.

Discovery of a 105-ms X-ray Pulsar in Kesteven-79: On the Nature of Compact Central Objects in Supernova Remnants

Abstract: We report the discovery of 105-ms X-ray pulsations from the compact central object (CCO) in the supernova remnant \snr\ using data acquired with the {\it Newton X-Ray Multi-Mirror Mission). Using two observations of the pulsar taken 6-days apart we derive an upper limit on its spin-down rate of $\dot P 18.5$-kyr. The latter exceeds the remnant's estimated age, suggesting that the pulsar was born spinning near its current period. The X-ray spectrum of \psr\ is best characterized as a blackbody of temperature $kT {BB) =, 0.43\pm0.02$ keV, radius $R-{BB) \approx 1.3$-km, and $~I{\rm bol) = 5.2 \times 10A{33)$ ergs-sSA{-1)$ at $d = 7.1$-kpc. The sinusoidal light curve is modulated with a pulsed fraction of $>45\%$, suggestive of a small hot spot on the surface of the rotating neutron star. The lack of a discernible pulsar wind nebula is consistent with an interpretation of \psr\ as a rotation-powered pulsar whose spin-down luminosity falls below the empirical threshold for generating bright wind nebulae, $\dot E-{\rm c) = 4 \times 10A{36)$-ergs-sSA{-I)$. The age discrepancy suggests that its $\dot E$ has always been below $\dot E c$, perhaps a distinguishing property of the CCOs. Alternatively, the X-ray spectrum of \psr\ suggests a low-luminosity AXP, but the weak inferred $B-{\rm p)$ field is incompatible with a magnetar theory of its X-ray luminosity. The ordinary spin parameters discovered from \psr\ highlight the inability of existing theories to explain the high luminosities and temperatures of CCO thermal X-ray spectra.