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Search Results: 1 - 10 of 4290 matches for " Karl Stapelfeldt "
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The Optical-nir Opacity Law in yso Disks and Envelopes: Evidence for Dust Growth?
Alan M. Watson,Karl R. Stapelfeldt
Revista mexicana de astronomía y astrofísica , 2005,
The Optical-NIR Opacity Law in YSO Disks and Envelopes: Evidence for Dust Growth?
Alan M. Watson,Karl R. Stapelfeldt
Revista mexicana de astronomía y astrofísica , 2004,
The Circumstellar Disk of the Butterfly Star in Taurus
Sebastian Wolf,Deborah L. Padgett,Karl R. Stapelfeldt
Physics , 2003, DOI: 10.1086/374041
Abstract: We present a model of the circumstellar environment of the so-called ``Butterfly Star'' in Taurus (IRAS 04302+2247). The appearance of this young stellar object is dominated by a large circumstellar disk seen edge-on and the light scattering lobes above the disk. The model is based on multi-wavelength continuum observations: Millimeter maps and high-resolution near-infrared images obtained with HST/NICMOS. It was found that the disk and envelope parameters are comparable with those of the circumstellar environment of other young stellar objects. A main result is that the dust properties must be different in the circumstellar disk and in the envelope: While a grain size distribution with grain radii up to 100 micron is required to reproduce the millimeter observations of the disk, the envelope is dominated by smaller grains similar to those of the interstellar medium. Preprint with high figure quality available at: http://spider.ipac.caltech.edu/staff/swolf/homepage/public/preprints/i04302.ps
A dim candidate companion to εCephei
Dimitri Mawet,Bertrand Mennesson,Eugene Serabyn,Karl Stapelfeldt,Olivier Absil
Physics , 2011, DOI: 10.1088/2041-8205/738/1/L12
Abstract: Using a vector vortex coronagraph behind the 1.5-m well-corrected subaperture (WCS) at Palomar, we detected a second object very close to \epsilon Cephei, a \delta Scuti F0 IV star. The candidate companion, ~50 times fainter than \epsilon Cephei, if physically associated, is a late-type K or early M star, and lies at an angular separation of 330 mas, or 1.1 \lambda/D for the WCS, making it the smallest angle detection ever realized with a coronagraph in terms of \lambda/D units. The projected separation of the putative companion is ~8.6 AU, most likely on a highly eccentric orbit. The recently detected near-infrared excess is thus likely not due to hot dust. Moreover, we also show that the previously reported IRAS 60 \mu m excess was due to source confusion on the galactic plane.
A Mid-Infrared Search for Substellar Companions of Nearby Planet-Host Stars
Alan Hulsebus,Massimo Marengo,Joe Carson,Karl Stapelfeldt
Physics , 2014, DOI: 10.1088/0004-637X/784/1/41
Abstract: Determining the presence of widely separated substellar-mass companion is crucial to understand the dynamics of inner planets in extrasolar planetary systems (e.g. to explain their high mean eccentricity as inner planets are perturbed by the Kozai mechanism). We report the results of our $\textit{Spitzer}$/Infrared Array Camera (IRAC) imaging search for widely separated (10 to 25$^{\prime\prime}$) substellar-mass companions for 14 planet-host stars within 15 pc of the Sun. Using deep 3.6 and 4.5 $\mu$m observations in subarray mode, we found one object in the field of 47 UMa with [3.6]$-$[4.5] color similar to a T5 dwarf, which is, however, unlikely to share common proper motion with 47 UMa. We also found three objects with brown-dwarf-like [3.6]$-$[4.5] color limits in the fields of GJ 86, HD 160691, and GJ 581, as well as another in the field of HD 69830 for which we have excluded common proper motion. We provide model-based upper mass limits for unseen objects around all stars in our sample, with typical sensitivity to 10 M$_{J}$ objects from a projected separation of 50 to 300 au from the parent star. We also discuss our data analysis methods for point-spread-function subtraction, image co-alignment, and artifact subtraction of IRAC subarray images.
Hubble Space Telescope Observations of the HD 202628 Debris Disk
John E. Krist,Karl R. Stapelfeldt,Geoffrey Bryden,Peter Plavchan
Physics , 2012, DOI: 10.1088/0004-6256/144/2/45
Abstract: A ring-shaped debris disk around the G2V star HD 202628 (d = 24.4 pc) was imaged in scattered light at visible wavelengths using the coronagraphic mode of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The ring is inclined by 64 degrees from face-on, based on the apparent major/minor axis ratio, with the major axis aligned along PA = 130 degrees. It has inner and outer radii (>50% maximum surface brightness) of 139 AU and 193 AU in the northwest ansae and 161 AU and 223 AU in the southeast (dr/r ~ 0.4). The maximum visible radial extent is ~254 AU. With a mean surface brightnesses of V ~ 24 mag per square arcsec, this is the faintest debris disk observed to date in reflected light. The center of the ring appears offset from the star by ~28 AU (deprojected). An ellipse fit to the inner edge has an eccentricity of 0.18 and a = 158 AU. This offset, along with the relatively sharp inner edge of the ring, suggests the influence of a planetary-mass companion. There is a strong similarity with the debris ring around Fomalhaut, though HD 202628 is a more mature star with an estimated age of about 2 Gyr. We also provide surface brightness limits for nine other stars in our study with strong Spitzer excesses around which no debris disks were detected in scattered light (HD 377, HD 7590, HD 38858, HD 45184, HD 73350, HD 135599, HD 145229, HD 187897, and HD 201219).
The WISE Census of Young Stellar Objects in Canis Major
William J. Fischer,Deborah L. Padgett,Karl R. Stapelfeldt
Physics , 2015,
Abstract: While searches for young stellar objects (YSOs) with the Spitzer Space Telescope focused on known molecular clouds, photometry from the Wide-field Infrared Survey Explorer (WISE) can be used to extend the search to the entire sky. As a precursor to more expansive searches, we present results for a 100 square degree region centered on the Canis Major clouds.
Characterizing Rocky and Gaseous Exoplanets with 2-meter Class Space-based Coronagraphs
Tyler D. Robinson,Karl R. Stapelfeldt,Mark S. Marley
Physics , 2015,
Abstract: Several concepts now exist for small, space-based missions to directly characterize exoplanets in reflected light. Here, we develop an instrument noise model suitable for studying the spectral characterization potential of a coronagraph-equipped, space-based telescope. We adopt a baseline set of telescope and instrument parameters appropriate for near-future planned missions like WFIRST-AFTA, including a 2 m diameter primary aperture, an operational wavelength range of 0.4-1.0 um, and an instrument spectral resolution of 70, and apply our baseline model to a variety of spectral models of different planet types, including Earth twins, Jupiter twins, and warm and cool Jupiters and Neptunes. With our exoplanet spectral models, we explore wavelength-dependent planet-star flux ratios for main sequence stars of various effective temperatures, and discuss how coronagraph inner and outer working angle constraints will influence the potential to study different types of planets. For planets most favorable to spectroscopic characterization, we study the integration times required to achieve moderate signal-to-noise ratio spectra. We also explore the sensitivity of the integration times required to either detect the bottom or presence of key absorption bands to coronagraph raw contrast performance, exozodiacal light levels, and the distance to the planetary system. Decreasing detector quantum efficiency at longer visible wavelengths makes the detection of water vapor in the atmospheres of Earth-like planets extremely challenging, and also hinders detections of the 0.89 um methane band. Additionally, most modeled observations have noise dominated by dark current, indicating that improving CCD performance could substantially drive down requisite integration times. Finally, we briefly discuss the extension of our models to a more distant future Large UV-Optical-InfraRed (LUVOIR) mission.
The Photometric Variability of HH 30
Watson, Alan M.;Durán-Rojas, Maria Carolina;Stapelfeldt, Karl R.;
Revista mexicana de astronomía y astrofísica , 2008,
Abstract: hh 30 is an edge-on disk around a young stellar object. previous imaging with the hubble space telescope has show morphological variability that is possibly related to the rotation of the star or the disk. we report the results of two terrestrial observing campaigns to monitor the integrated magnitude of hh 30. we use the lomb-scargle periodogram to look for periodic modulation with periods between 2 days and almost 90 days in these two data sets and in a third, previously published, data set. we develop a method to deal with short-term correlations in the data. our results indicate that none of the data sets shows evidence for significant periodic photometric modulation.
HST/NICMOS Imaging of Disks and Envelopes Around Very Young Stars
Deborah L. Padgett,Wolfgang Brandner,Karl R. Stapelfeldt,Stephen E. Strom,Susan Terebey,David Koerner
Physics , 1999, DOI: 10.1086/300781
Abstract: We present HST/NICMOS observations with 0.1" (15 AU) resolution of six young stellar objects in the Taurus star-formation region. The targets of our survey are three Class I IRAS sources (IRAS 04016+2610, IRAS 04248+2612, and IRAS 04302+2247) and three low-luminosity stars (DG Tau B, Haro 6-5B, and CoKu Tau/1) associated with Herbig Haro jets. The broad-band images show that the near-infrared radiation from these sources is dominated by light scattered from dusty circumstellar material distributed in a region 10 - 15 times the size of our solar system. Although the detailed morphologies of the individual objects are unique, the observed young stellar objects share common features. All of the circumstellar reflection nebulae are crossed by dark lanes from 500 - 900 AU in extent and from less than 50 to 350 AU in apparent thickness. The absorption lanes extend perpendicular to known optical and millimeter outflows in these sources. We interpret the dark lanes as optically thick circumstellar disks seen in silhouette against bright reflection nebulosity. The bipolar reflection nebulae extending perpendicular to the dust lanes appear to be produced by scattering from the upper and lower surfaces of the disks and from dusty material within or on the walls of the outflow cavities. Out of five objects in which the central source is directly detected, two are found to be subarcsecond binaries. This mini-survey is the highest resolution near-infrared study to date of circumstellar environments around solar-type stars with age <= 1 Myr.
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