We have used the Spitzer Space Telescope Infrared Spectrograph (IRS) to observe the 5-37 µm therm... more We have used the Spitzer Space Telescope Infrared Spectrograph (IRS) to observe the 5-37 µm thermal emission of comet 73P/Schwassmann-Wachmann 3 (SW3), components B and C. We obtained low spectral resolution (R∼100) data over the entire wavelength interval, along with images at 16 and 22 µm. These observations provided an unprecedented opportunity to study nearly pristine material from the surface and what was until recently the interior of an ecliptic comet-cometary surface having experienced only two prior perihelion passages, and including material that was totally fresh. The spectra were modeled using a variety of mineral types including both amorphous and crystalline components. We find that the degree of silicate crystallinity, ∼35%, is somewhat lower than most other comets with strong emission features, while its abundance of amorphous carbon is higher. Both suggest that SW3 is among the most chemically primitive solar system objects yet studied in detail, and that it formed earlier or farther from the sun than the bulk of the comets studied so far. The similar dust compositions of the two fragments suggests that these are not mineralogically heterogeneous, but rather uniform throughout their volumes. The best-fit particle size distribution for SW3B has a form dn/da∼a −3.5 , close to that expected for dust in collisional equilibrium, while that for SW3C has dn/da∼a −4.0 , as seen mostly in active comets with strong directed jets such as C/1995 O1 Hale-Bopp. The total mass of dust in the comae plus nearby tail, extrapolated from to the field of view of the IRS peakup image arrays, is 3-5 x 10 8 kg for B and 7-9 x 10 8
Using the NASA/IRTF SpeX & BASS spectrometers we have obtained 0.7-13 µm observations of the newl... more Using the NASA/IRTF SpeX & BASS spectrometers we have obtained 0.7-13 µm observations of the newly imaged HD36546 debris disk system. The SpeX spectrum is most consistent with the photospheric emission expected from an L * ~ 20 L ! , solar abundance A1.5V star with little to no extinction, and excess emission from circumstellar dust detectable beyond 4.5 µm. Non-detections of CO emission lines and accretion signatures point to the gas-poor circumstellar environment of a very old transition disk. Combining the SpeX + BASS spectra with archival WISE/AKARI/IRAS/Herschel photometry, we find an outer cold dust belt at ~135K and 20-40 AU from the primary, likely coincident with the disk imaged by Subaru (Currie et al. 2017), and a new second inner belt with temperature ~570K and an unusual, broad SED maximum in the 6-9 µm region, tracing dust at 1.1-2.2 AU. An SED maximum at 6-9 µm has been reported in just two other A-star systems, HD131488 and HD121191, both of ~10 Myr age (Melis et al. 2013). From Spitzer, we have also identified the ~12 Myr old A7V HD148567 system as having similar 5-35 µm excess spectral features (Mittal et al. 2015). The Spitzer data allows us to rule out water emission and rule in carbonaceous materials-organics, carbonates, SiC-as the source of the 6-9 µm excess. Assuming a common origin for the 4 young A-star systems' disks, we suggest they are experiencing an early era of carbon-rich planetesimal processing.
This publication provides guidelines for conducting radiometric calibrations of electro-optical (... more This publication provides guidelines for conducting radiometric calibrations of electro-optical (EO) sensors. It is intended for use by managers, technical oversight personnel, scientists, and engineers as a reference for planning and successfully executing sensor calibrations. This document is a collaborative effort between the US government, academic institutions, and industry, and represents lessons learned from experts with years of accumulated knowledge and experience planning, reviewing, preparing, conducting, analyzing, implementing, and reporting calibration efforts. Technical terms and definitions are introduced as needed throughout the document. Important terms, acronyms, and common references used in this text are summarized in the glossary at the end of the publication.
We present the first resolved near-infrared imagery of the transition disk Oph IRS 48 (WLY 2-48),... more We present the first resolved near-infrared imagery of the transition disk Oph IRS 48 (WLY 2-48), which was recently observed with ALMA to have a strongly asymmetric submillimeter flux distribution. H-band polarized intensity images show a ∼60 AU radius scattered light cavity with two pronounced arcs of emission, one from northeast to southeast and one smaller, fainter, and more distant arc in the northwest. K-band scattered light imagery reveals a similar morphology, but with a clear third arc along the southwestern rim of the disk cavity. This arc meets the northwestern arc at nearly a right angle, revealing the presence of a spiral arm or local surface brightness deficit in the disk, and explaining the east-west brightness asymmetry in the H-band data. We also present 0.8-5.4 μm IRTF SpeX spectra of this object, which allow us to constrain the spectral class to A0 ± 1 and measure a low mass accretion rate of 10 −8.5 M yr −1 , both consistent with previous estimates. We investigate a variety of reddening laws in order to fit the multiwavelength spectral energy distribution of Oph IRS 48 and find a best fit consistent with a younger, higher luminosity star than previous estimates.
Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-... more Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-polarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use Hubble Space Telescope (HST)/STIS coronagraphic imagery to measure the V magnitude of the star for both STIS coronagraphic observations, compare these data with optical photometry in the literature, and find that, unlike other classical T Tauri stars observed in the same HST program, the disk is most robustly detected in scattered light at stellar optical minimum light. We measure the outer disk radius, 1. 15 ± 0. 10, major-axis position angle, and disk inclination and find that the inner disk, as reported in the literature, is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet, detected in both STIS observations and in follow-on Goddard Fabry-Perot imagery, which is also misaligned with respect to the projection of the outer disk minor axis and is poorly collimated near the star, but which can be traced 21 from the star in data from 2005. The measured outer disk inclination, 71 • ± 1 • , is out of the range of inclinations suggested for stars with UX-Orionis-like variability when no grain growth has occurred in the disk. The faintness of the disk, small disk size, and detection of the star despite the high inclination all indicate that the dust disk must have experienced grain growth and settling toward the disk midplane, which we verify by comparing the observed disk with model imagery from the literature.
The Broadband Array Spectrograph System with the NASA Infrared Telescope Facility was used to obt... more The Broadband Array Spectrograph System with the NASA Infrared Telescope Facility was used to obtain 3- to 13-micron spectra of Io on June 14-16, 1991. The extinction correction and its error for each standard star (Alpha Boo, Alpha Lyr, and Mu UMa) were found individually by performing an unweighted linear fit of instrumental magnitude as a function of airmass. The
We report 3-13 micron spectroscopyy of comet 55P/Tempel-Tuttle on Feb 8 and 9 1998 UT (roughly th... more We report 3-13 micron spectroscopyy of comet 55P/Tempel-Tuttle on Feb 8 and 9 1998 UT (roughly three weeks before perihelion) using the NASA Infrared Telescope Facility and The Aerospace Corporation Broadband Array Spectrograph System (BASS) with a ...
These are exciting times in the study f planetary system f rmati n, with a steadily expanding inv... more These are exciting times in the study f planetary system f rmati n, with a steadily expanding invent ry f ex planet detecti ns and imaging f dust disks ar und nearby y ung and main-sequence stars. Alth ugh these disc veriesimplythat urs larsystemisfarfr munique, ...
As part of a survey of the mid-IR spectral characteristics of stars with circumstellar dust disks... more As part of a survey of the mid-IR spectral characteristics of stars with circumstellar dust disks (Herbig Ae/Be stars, T Tauri stars, and a few other objects with similar characteristics) we have been monitoring a few select object for variability. In a few cases, such as the isolated ...
We describe a concept for a new imaging spectrograph operating in the mid-wave and long-wave infr... more We describe a concept for a new imaging spectrograph operating in the mid-wave and long-wave infrared. The instrument is proposed as an upgrade to The Aerospace Corporation's Broadband Array Spectrograph System (BASS), a 3-13 micron sensor currently in use on the Advanced Electro-Optical System (AEOS) 3.67 meter telescope. The primary tasks of the instrument would be to generate precise spectrophotometry
We analyze 3 epochs of ultraviolet (UV), optical and near-infrared (NIR) observations of the Taur... more We analyze 3 epochs of ultraviolet (UV), optical and near-infrared (NIR) observations of the Taurus transitional disk GM Aur using the Hubble Space Telescope Imaging Spectrograph (STIS) and the Infrared Telescope Facility SpeX spectrograph. Observations were separated by one week and 3 months in order to study variability over multiple timescales. We calculate accretion rates for each epoch of observations using the STIS spectra and find that those separated by one week had similar accretion rates (∼ 1 × 10 −8 M ⊙ yr −1) while the epoch obtained 3 months later had a substantially lower accretion rate (∼ 4 × 10 −9 M ⊙ yr −1). We find that the decline in accretion rate is caused by lower densities of material in the accretion flows, as opposed to a lower surface coverage of the accretion columns. During the low accretion rate epoch we also observe lower fluxes at both far UV (FUV) and IR wavelengths, which trace molecular gas and dust in the disk, respectively. We find that this can be explained by a lower dust and gas mass in the inner disk. We attribute the observed variability to inhomogeneities in the inner disk, near the corotation radius, where gas and dust may co-exist near the footprints of the magnetospheric flows. These FUV-NIR data offer a new perspective on the structure of the inner disk, the stellar magnetosphere, and their interaction.
We report 3 - 13 micron spectroscopy of 4 comets observed between August 2002 and February 2003: ... more We report 3 - 13 micron spectroscopy of 4 comets observed between August 2002 and February 2003: C/2002 O4 (Honig) on August 1, 2002, C/2002 V1 (NEAT) on Jan. 9 and 10, 2003, C/2002 X5 (Kudo-Fujikawa) on Jan. 9 and 10, 2003, and C/2002 Y1 (Juels-Holvorcem) on Feb. 20, 2003. In addition, we include data obtained much earlier on 69P/Taylor (February 9, 1998) but not previously published. For Comets Taylor, Honig, NEAT, and Kudo-Fujikawa, the silicate emission band was detected, being approximately 23%, 12%, 15%, and 10%, respectively, above the continuum. The data for Comet Juels-Holvorcem were of insufficient quality to detect the presence of a silicate band of comparable strength to the other three objects, and we place an upper limit of 24% on this feature. The silicate features in both NEAT and Kudo-Fujikawa contained structure indicating the presence of crystalline material. Combining these data with those of other comets, we confirm the correlation between silicate band strength...
Infrared photometry and spectroscopy covering a time span of a quarter century are presented for ... more Infrared photometry and spectroscopy covering a time span of a quarter century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically in its inner disk region, with the
We present thirteen epochs of near-infrared (0.8-5 µm) spectroscopic observations of the pre-tran... more We present thirteen epochs of near-infrared (0.8-5 µm) spectroscopic observations of the pre-transitional, "gapped" disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (Brα, Brγ, Paβ, Paγ, Paδ, Paǫ, and the 0.8446 µm line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 x 10 -8 M ⊙ yr -1 was derived from the Brγ and Paβ lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only ∼30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 µm was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on time scales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magnetorotational) would operate there on longer time scales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via Guest Observer,
We have used the Spitzer Space Telescope Infrared Spectrograph (IRS) to observe the 5-37 µm therm... more We have used the Spitzer Space Telescope Infrared Spectrograph (IRS) to observe the 5-37 µm thermal emission of comet 73P/Schwassmann-Wachmann 3 (SW3), components B and C. We obtained low spectral resolution (R∼100) data over the entire wavelength interval, along with images at 16 and 22 µm. These observations provided an unprecedented opportunity to study nearly pristine material from the surface and what was until recently the interior of an ecliptic comet-cometary surface having experienced only two prior perihelion passages, and including material that was totally fresh. The spectra were modeled using a variety of mineral types including both amorphous and crystalline components. We find that the degree of silicate crystallinity, ∼35%, is somewhat lower than most other comets with strong emission features, while its abundance of amorphous carbon is higher. Both suggest that SW3 is among the most chemically primitive solar system objects yet studied in detail, and that it formed earlier or farther from the sun than the bulk of the comets studied so far. The similar dust compositions of the two fragments suggests that these are not mineralogically heterogeneous, but rather uniform throughout their volumes. The best-fit particle size distribution for SW3B has a form dn/da∼a −3.5 , close to that expected for dust in collisional equilibrium, while that for SW3C has dn/da∼a −4.0 , as seen mostly in active comets with strong directed jets such as C/1995 O1 Hale-Bopp. The total mass of dust in the comae plus nearby tail, extrapolated from to the field of view of the IRS peakup image arrays, is 3-5 x 10 8 kg for B and 7-9 x 10 8
Using the NASA/IRTF SpeX & BASS spectrometers we have obtained 0.7-13 µm observations of the newl... more Using the NASA/IRTF SpeX & BASS spectrometers we have obtained 0.7-13 µm observations of the newly imaged HD36546 debris disk system. The SpeX spectrum is most consistent with the photospheric emission expected from an L * ~ 20 L ! , solar abundance A1.5V star with little to no extinction, and excess emission from circumstellar dust detectable beyond 4.5 µm. Non-detections of CO emission lines and accretion signatures point to the gas-poor circumstellar environment of a very old transition disk. Combining the SpeX + BASS spectra with archival WISE/AKARI/IRAS/Herschel photometry, we find an outer cold dust belt at ~135K and 20-40 AU from the primary, likely coincident with the disk imaged by Subaru (Currie et al. 2017), and a new second inner belt with temperature ~570K and an unusual, broad SED maximum in the 6-9 µm region, tracing dust at 1.1-2.2 AU. An SED maximum at 6-9 µm has been reported in just two other A-star systems, HD131488 and HD121191, both of ~10 Myr age (Melis et al. 2013). From Spitzer, we have also identified the ~12 Myr old A7V HD148567 system as having similar 5-35 µm excess spectral features (Mittal et al. 2015). The Spitzer data allows us to rule out water emission and rule in carbonaceous materials-organics, carbonates, SiC-as the source of the 6-9 µm excess. Assuming a common origin for the 4 young A-star systems' disks, we suggest they are experiencing an early era of carbon-rich planetesimal processing.
This publication provides guidelines for conducting radiometric calibrations of electro-optical (... more This publication provides guidelines for conducting radiometric calibrations of electro-optical (EO) sensors. It is intended for use by managers, technical oversight personnel, scientists, and engineers as a reference for planning and successfully executing sensor calibrations. This document is a collaborative effort between the US government, academic institutions, and industry, and represents lessons learned from experts with years of accumulated knowledge and experience planning, reviewing, preparing, conducting, analyzing, implementing, and reporting calibration efforts. Technical terms and definitions are introduced as needed throughout the document. Important terms, acronyms, and common references used in this text are summarized in the glossary at the end of the publication.
We present the first resolved near-infrared imagery of the transition disk Oph IRS 48 (WLY 2-48),... more We present the first resolved near-infrared imagery of the transition disk Oph IRS 48 (WLY 2-48), which was recently observed with ALMA to have a strongly asymmetric submillimeter flux distribution. H-band polarized intensity images show a ∼60 AU radius scattered light cavity with two pronounced arcs of emission, one from northeast to southeast and one smaller, fainter, and more distant arc in the northwest. K-band scattered light imagery reveals a similar morphology, but with a clear third arc along the southwestern rim of the disk cavity. This arc meets the northwestern arc at nearly a right angle, revealing the presence of a spiral arm or local surface brightness deficit in the disk, and explaining the east-west brightness asymmetry in the H-band data. We also present 0.8-5.4 μm IRTF SpeX spectra of this object, which allow us to constrain the spectral class to A0 ± 1 and measure a low mass accretion rate of 10 −8.5 M yr −1 , both consistent with previous estimates. We investigate a variety of reddening laws in order to fit the multiwavelength spectral energy distribution of Oph IRS 48 and find a best fit consistent with a younger, higher luminosity star than previous estimates.
Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-... more Previous studies of the classical T Tauri star AA Tau have interpreted the UX-Orionis-like photo-polarimetric variability as being due to a warp in the inner disk caused by an inclined stellar magnetic dipole field. We test that these effects are macroscopically observable in the inclination and alignment of the disk. We use Hubble Space Telescope (HST)/STIS coronagraphic imagery to measure the V magnitude of the star for both STIS coronagraphic observations, compare these data with optical photometry in the literature, and find that, unlike other classical T Tauri stars observed in the same HST program, the disk is most robustly detected in scattered light at stellar optical minimum light. We measure the outer disk radius, 1. 15 ± 0. 10, major-axis position angle, and disk inclination and find that the inner disk, as reported in the literature, is both misinclined and misaligned with respect to the outer disk. AA Tau drives a faint jet, detected in both STIS observations and in follow-on Goddard Fabry-Perot imagery, which is also misaligned with respect to the projection of the outer disk minor axis and is poorly collimated near the star, but which can be traced 21 from the star in data from 2005. The measured outer disk inclination, 71 • ± 1 • , is out of the range of inclinations suggested for stars with UX-Orionis-like variability when no grain growth has occurred in the disk. The faintness of the disk, small disk size, and detection of the star despite the high inclination all indicate that the dust disk must have experienced grain growth and settling toward the disk midplane, which we verify by comparing the observed disk with model imagery from the literature.
The Broadband Array Spectrograph System with the NASA Infrared Telescope Facility was used to obt... more The Broadband Array Spectrograph System with the NASA Infrared Telescope Facility was used to obtain 3- to 13-micron spectra of Io on June 14-16, 1991. The extinction correction and its error for each standard star (Alpha Boo, Alpha Lyr, and Mu UMa) were found individually by performing an unweighted linear fit of instrumental magnitude as a function of airmass. The
We report 3-13 micron spectroscopyy of comet 55P/Tempel-Tuttle on Feb 8 and 9 1998 UT (roughly th... more We report 3-13 micron spectroscopyy of comet 55P/Tempel-Tuttle on Feb 8 and 9 1998 UT (roughly three weeks before perihelion) using the NASA Infrared Telescope Facility and The Aerospace Corporation Broadband Array Spectrograph System (BASS) with a ...
These are exciting times in the study f planetary system f rmati n, with a steadily expanding inv... more These are exciting times in the study f planetary system f rmati n, with a steadily expanding invent ry f ex planet detecti ns and imaging f dust disks ar und nearby y ung and main-sequence stars. Alth ugh these disc veriesimplythat urs larsystemisfarfr munique, ...
As part of a survey of the mid-IR spectral characteristics of stars with circumstellar dust disks... more As part of a survey of the mid-IR spectral characteristics of stars with circumstellar dust disks (Herbig Ae/Be stars, T Tauri stars, and a few other objects with similar characteristics) we have been monitoring a few select object for variability. In a few cases, such as the isolated ...
We describe a concept for a new imaging spectrograph operating in the mid-wave and long-wave infr... more We describe a concept for a new imaging spectrograph operating in the mid-wave and long-wave infrared. The instrument is proposed as an upgrade to The Aerospace Corporation's Broadband Array Spectrograph System (BASS), a 3-13 micron sensor currently in use on the Advanced Electro-Optical System (AEOS) 3.67 meter telescope. The primary tasks of the instrument would be to generate precise spectrophotometry
We analyze 3 epochs of ultraviolet (UV), optical and near-infrared (NIR) observations of the Taur... more We analyze 3 epochs of ultraviolet (UV), optical and near-infrared (NIR) observations of the Taurus transitional disk GM Aur using the Hubble Space Telescope Imaging Spectrograph (STIS) and the Infrared Telescope Facility SpeX spectrograph. Observations were separated by one week and 3 months in order to study variability over multiple timescales. We calculate accretion rates for each epoch of observations using the STIS spectra and find that those separated by one week had similar accretion rates (∼ 1 × 10 −8 M ⊙ yr −1) while the epoch obtained 3 months later had a substantially lower accretion rate (∼ 4 × 10 −9 M ⊙ yr −1). We find that the decline in accretion rate is caused by lower densities of material in the accretion flows, as opposed to a lower surface coverage of the accretion columns. During the low accretion rate epoch we also observe lower fluxes at both far UV (FUV) and IR wavelengths, which trace molecular gas and dust in the disk, respectively. We find that this can be explained by a lower dust and gas mass in the inner disk. We attribute the observed variability to inhomogeneities in the inner disk, near the corotation radius, where gas and dust may co-exist near the footprints of the magnetospheric flows. These FUV-NIR data offer a new perspective on the structure of the inner disk, the stellar magnetosphere, and their interaction.
We report 3 - 13 micron spectroscopy of 4 comets observed between August 2002 and February 2003: ... more We report 3 - 13 micron spectroscopy of 4 comets observed between August 2002 and February 2003: C/2002 O4 (Honig) on August 1, 2002, C/2002 V1 (NEAT) on Jan. 9 and 10, 2003, C/2002 X5 (Kudo-Fujikawa) on Jan. 9 and 10, 2003, and C/2002 Y1 (Juels-Holvorcem) on Feb. 20, 2003. In addition, we include data obtained much earlier on 69P/Taylor (February 9, 1998) but not previously published. For Comets Taylor, Honig, NEAT, and Kudo-Fujikawa, the silicate emission band was detected, being approximately 23%, 12%, 15%, and 10%, respectively, above the continuum. The data for Comet Juels-Holvorcem were of insufficient quality to detect the presence of a silicate band of comparable strength to the other three objects, and we place an upper limit of 24% on this feature. The silicate features in both NEAT and Kudo-Fujikawa contained structure indicating the presence of crystalline material. Combining these data with those of other comets, we confirm the correlation between silicate band strength...
Infrared photometry and spectroscopy covering a time span of a quarter century are presented for ... more Infrared photometry and spectroscopy covering a time span of a quarter century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically in its inner disk region, with the
We present thirteen epochs of near-infrared (0.8-5 µm) spectroscopic observations of the pre-tran... more We present thirteen epochs of near-infrared (0.8-5 µm) spectroscopic observations of the pre-transitional, "gapped" disk system in SAO 206462 (=HD 135344B). In all, six gas emission lines (Brα, Brγ, Paβ, Paγ, Paδ, Paǫ, and the 0.8446 µm line of O I) along with continuum measurements made near the standard J, H, K, and L photometric bands were measured. A mass accretion rate of approximately 2 x 10 -8 M ⊙ yr -1 was derived from the Brγ and Paβ lines. However, the fluxes of these lines varied by a factor of over two during the course of a few months. The continuum also varied, but by only ∼30%, and even decreased at a time when the gas emission was increasing. The H I line at 1.083 µm was also found to vary in a manner inconsistent with that of either the hydrogen lines or the dust. Both the gas and dust variabilities indicate significant changes in the region of the inner gas and the inner dust belt that may be common to many young disk systems. If planets are responsible for defining the inner edge of the gap, they could interact with the material on time scales commensurate with what is observed for the variations in the dust, while other disk instabilities (thermal, magnetorotational) would operate there on longer time scales than we observe for the inner dust belt. For SAO 206462, the orbital period would likely be 1-3 years. If the changes are being induced in the disk material closer to the star than the gap, a variety of mechanisms (disk instabilities, interactions via Guest Observer,
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