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Browsing by Author "Silverstone, MD"

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    The circumstellar disk of HD 141569 imaged with NICMOS
    (University of Chicago Press, 1999-10-05) Weinberger, AJ; Becklin, EE; Schneider, G; Smith, BA; Lowrance, PJ; Silverstone, MD; Zuckerman, B; Terrile, RJ; University of California System; University of California Los Angeles; University of Arizona; University of Hawaii System; California Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Jet Propulsion Laboratory (JPL); University of Alabama Tuscaloosa
    Coronagraphic imaging with the Near-Infrared Camera and Multiobject Spectrometer on the Hubble Space Telescope reveals a large, similar to 400 AU (4") radius, circumstellar disk around the Herbig Ac/Be star HD 141569. A reflected light image at 1.1 Ccm shows the disk oriented at a position angle of 356 degrees +/- 5 degrees and inclined to our line of sight by 51 degrees +/- 3 degrees; the intrinsic scattering function of the dust in the disk makes the side inclined toward us, the eastern side, brighter. The disk flux density peaks 185 AU (1".85) from the star and falls off to both larger and smaller radii. A region of depleted material, or a gap, in the disk is centered 250 AU from the star. The dynamical effect of one or more planets may be necessary to explain this morphology.
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    Discovery of a nearly edge-on disk around HD 32297
    (IOP Publishing, 2005-08-20) Schneider, G; Silverstone, MD; Hines, DC; University of Arizona; University of Alabama Tuscaloosa
    We report the discovery of a nearly edge-on disk about the A0 star HD 32297 seen in light scattered by the disk grains revealed in NICMOS PSF-subtracted coronagraphic images. The disk extends to a distance of at least 400 AU (3".3) along its major axis with a 1.1 mu m flux density of 4.81 +/- 0.57 mJy beyond a radius of 0".3 from the coronagraphically occulted star. The fraction of 1.1 mu m starlight scattered by the disk, 0.0033 +/- 0.0004, is comparable to its fractional excess emission at 25 + 60 mu m of similar to 0.0027 as measured from IRAS data. The disk appears to be inclined 10 degrees.5 +/- 2 degrees.5 from an edge-on viewing geometry, with its major axis oriented 236 degrees.5 +/- 1 degrees eastward of north. The disk exhibits unequal brightness on opposing sides and a break in the surface brightness profile along the NE-side disk major axis. Such asymmetries might implicate the existence of one or more (unseen) planetary mass companions.
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    Dusty debris around solar-type stars: Temporal disk evolution
    (University of Chicago Press, 2001) Spangler, C; Sargent, AI; Silverstone, MD; Becklin, EE; Zuckerman, B; California Institute of Technology; University of California System; University of California Los Angeles; University of Alabama Tuscaloosa
    Using ISO-ISOPHOT, we carried out a survey of almost 150 stars to search for evidence of emission from dust orbiting young main-sequence stars, both in clusters and isolated systems. Over half of the detections are new examples of dusty stellar systems and demonstrate that such dust can be detected around numerous stars older than a few times 10(6) yr. Fluxes at 60 and either 90 or 100 mum for the new excess sources together with improved fluxes for a number of IRAS-identified sources are presented. Analysis of the excess luminosity relative to the stellar photosphere shows a systematic decline of this excess with stellar age consistent with a power-law index of -2.
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    The formation and evolution of planetary systems (FEPS): Discovery of an unusual debris system associated with HD 12039
    (IOP Publishing, 2006-02-20) Hines, DC; Backman, DE; Bouwman, J; Hillenbrand, LA; Carpenter, JM; Meyer, MR; Kim, JS; Silverstone, MD; Rodmann, J; Wolf, S; Mamajek, EE; Brooke, TY; Padgett, DL; Henning, T; Moro-Martin, A; Stobie, E; Gordon, KD; Morrison, JE; Muzerolle, J; Su, KYL; National Aeronautics & Space Administration (NASA); Max Planck Society; California Institute of Technology; University of Arizona; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; Princeton University; University of Alabama Tuscaloosa
    We report the discovery of a debris system associated with the similar to 30 Myr old G3/5V star HD 12039 using Spitzer Space Telescope observations from 3.6-160 mu m. An observed infrared excess (L-IR/L-* = 1 x 10(-4)) above the expected photosphere for lambda greater than or similar to 14 mu m is fit by thermally emitting material with a color temperature of T similar to 110 K, warmer than the majority of debris disks identified to date around Sun-like stars. The object is not detected at 70 mu m with a 3 sigma upper limit 6 times the expected photospheric flux. The spectrum of the infrared excess can be explained by warm, optically thin material comprised of blackbody-like grains of size greater than or similar to 7 mu m that reside in a belt orbiting the star at 4-6 AU. An alternate model dominated by smaller grains, near the blowout size a similar to 0.5 mu m, located at 30-40 AU is also possible but requires the dust to have been produced recently, since such small grains will be expelled from the system by radiation pressure in approximately a few times 10(2) yr.
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    Formation and evolution of planetary systems: Cold outer disks associated with sun-like stars
    (IOP Publishing, 2005-10-10) Kim, JS; Hines, DC; Backman, DE; Hillenbrand, LA; Meyer, MR; Rodmann, J; Moro-Martin, A; Carpenter, JM; Silverstone, MD; Bouwman, J; Mamajek, EE; Wolf, S; Malhotra, R; Pascucci, I; Najita, J; Padgett, DL; Henning, T; Brooke, TY; Cohen, M; Strom, SE; Stobie, EB; Engelbracht, CW; Gordon, KD; Misselt, K; Morrison, JE; Muzerolle, J; Su, KYL; University of Arizona; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; California Institute of Technology; Max Planck Society; Princeton University; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; National Optical Astronomy Observatory; University of California System; University of California Berkeley; University of Alabama Tuscaloosa
    We present the discovery of debris systems around three Sun-like stars based on observations performed with the Spitzer Space Telescope as part of a Legacy Science Program, "The Formation and Evolution of Planetary Systems'' ( FEPS). We also confirm the presence of debris around two other stars. All the stars exhibit infrared emission in excess of the expected photospheres in the 70 mu m band but are consistent with photospheric emission at <= 33 mu m. This restricts the maximum temperature of debris in equilibrium with the stellar radiation to T < 70 K. We find that these sources are relatively old in the FEPS sample, in the age range 0.7 - 3 Gyr. On the basis of models of the spectral energy distributions, we suggest that these debris systems represent materials generated by collisions of planetesimal belts. We speculate on the nature of these systems through comparisons to our own Kuiper Belt, and on the possible presence of planet( s) responsible for stirring the system and ultimately releasing dust through collisions. We further report observations of a nearby star HD 13974 ( d 11 pc) that are indistinguishable from a bare photosphere at both 24 and 70 mu m. The observations place strong upper limits on the presence of any cold dust in this nearby system (L-IR/L-* < 10 (-5.2)).
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    The formation and evolution of planetary systems: First results from a Spitzer Legacy Science Program
    (University of Chicago Press, 2004-09) Meyer, MR; Hillenbrand, LA; Backman, DE; Beckwith, SVW; Bouwman, J; Brooke, TY; Carpenter, JM; Cohen, M; Gorti, U; Henning, T; Hines, DC; Hollenbach, D; Kim, JS; Lunine, J; Malhotra, R; Mamajek, EE; Metchev, S; Moro-Martin, A; Morris, P; Najita, J; Padgett, DL; Rodmann, J; Silverstone, MD; Soderblom, DR; Stauffer, JR; Stobie, EB; Strom, SE; Watson, DM; Weidenschilling, SJ; Wolf, S; Young, E; Engelbracht, CW; Gordon, KD; Misselt, K; Morrison, J; Muzerolle, J; Su, K; University of Arizona; California Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Ames Research Center; Space Telescope Science Institute; Johns Hopkins University; Max Planck Society; University of California System; University of California Berkeley; National Optical Astronomy Observatory; University of Rochester; University of Alabama Tuscaloosa
    We present 3-160 mum photometry obtained with the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) instruments for the first five targets from the Spitzer Space Telescope Legacy Science Program "Formation and Evolution of Planetary Systems'' and 4-35 mum spectrophotometry obtained with the Infrared Spectrograph (IRS) for two sources. We discuss in detail our observations of the debris disks surrounding HD 105 (G0 V, 30+/-10 Myr) and HD 150706 (G3 V, similar to700+/-300 Myr). For HD 105, possible interpretations include large bodies clearing the dust inside of 45 AU or a reservoir of gas capable of sculpting the dust distribution. The disk surrounding HD 150706 also exhibits evidence of a large inner hole in its dust distribution. Of the four survey targets without previously detected IR excess, spanning ages 30 Myr to 3 Gyr, the new detection of excess in just one system of intermediate age suggests a variety of initial conditions or divergent evolutionary paths for debris disk systems orbiting solar-type stars.
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    Mid-infrared images of the debris disk around HD 141569
    (University of Chicago Press, 2002-07-01) Marsh, KA; Silverstone, MD; Becklin, EE; Koerner, DW; Werner, MW; Weinberger, AJ; Ressler, ME; California Institute of Technology; University of Arizona; University of California System; University of California Los Angeles; University of Pennsylvania; National Aeronautics & Space Administration (NASA); NASA Jet Propulsion Laboratory (JPL); Carnegie Institution for Science; University of Alabama Tuscaloosa
    We have imaged the circumstellar debris disk around the A0 Ve/B9.5 Ve star HD 141569 ( D = 99 pc), at lambda = 12.5, 17.9, and 20.8 mum using the Keck II telescope, and confirm the general morphology from other recently published mid-infrared observations. Model fits to an assumed at radially symmetric dust disk yield an inclination i = 53degrees +/- 5degrees and a position angle of -6degrees +/- 4degrees for the tilt axis and indicate the presence of a depression in optical depth by a factor of about 4 within a radial distance of 30 AU (0".3) from the star. Such a depression is suggestive of a density depletion and is consistent with published spectral energy distributions that indicate the absence of a near-infrared excess even though a mid-infrared excess is present. Our mid-infrared results, in conjunction with previously published near-infrared scattering images, suggest that the two wavelength regimes are viewing, respectively, the inner and outer parts of a common disk structure, which is dominated by small ( probably submicron) grains throughout.
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    NICMOS coronagraphic observations of the GM Aurigae circumstellar disk
    (IOP Publishing, 2003-03) Schneider, G; Wood, K; Silverstone, MD; Hines, DC; Koerner, DW; Whitney, BA; Bjorkman, JE; Lowrance, PJ; University of Arizona; University of St Andrews; Northern Arizona University; University System of Ohio; University of Toledo; California Institute of Technology; University of Alabama Tuscaloosa
    We present Hubble Space Telescope Near Infrared Camera and Multi-Object Spectrometer (NICMOS) coronagraphic observations of the environment in the region of the young star-disk system GM Aurigae. Scattered near-infrared light in two spectral bands (F110W = 1.1 mum and F160W = 1.6 mum) trace the morphology of circumstellar dust to a distance of similar to700 AU from the star. An similar to300 AU radius outwardly flared disk inclined 50degrees-55degrees to the plane of the sky surrounded by a tenuous envelope is seen in the NICMOS images, confirming the size and suspected flared nature of the disk suggested by earlier CO and optical observations. The NICMOS images probe the disk region with spatial resolutions of similar to0."1 at radial distances of 0."35 to similar to4."5-5."0 from the largely unobscured (A(v) < 0.5) central star. The midplane of the disk 1.'' 3 from GM Aurigae is revealed in silhouette against the previously unseen lower portion of the illuminated disk along its minor axis ( as projected onto the sky). We comment on surface brightness profiles along the disk major and minor axes, as well as isophotal maps of the disk. From these photometric data we have measured the integrated flux density of the disk, beyond the instrumental inner radius of 0.'' 35, as 8.0 and 9.3 mJy (+/-20%) at F110W and F160W, respectively, corresponding to disk scattering fractions of L-disk/L* = 0.025 (+/-20%) in both bands. By fitting the photometric properties of the disk to a scattered-light model, we estimate the disk mass to be similar to 0.04 M-.. Additionally, we find two diffuse red polar lobes along the disk minor axis, likely the result of a bipolar outflow, at distances of +/-3.'' 8 from GM Aurigae (similar to 900 AU with our inferred inclination) with peak H-band surface brightnesses of similar to 14 mu Jy arcsec(-2). We also note the existence of a broad (similar to 3 '' wide) band of blue material within the NICMOS field of view, spatially coincident with and extending at least 12 '' from the northeast outer region of the disk major axis.