5 research outputs found
Wavelength-Dependent Extinction and Grain Sizes in Dippers
We have examined inter-night variability of K2-discovered Dippers that are
not close to being viewed edge-on, as determined from previously-reported ALMA
images, using the SpeX spectrograph and the NASA Infrared Telescope facility
(IRTF). The three objects observed were EPIC 203850058, EPIC 205151387, and
EPIC 204638512 (2MASS J16042165-2130284). Using the ratio of the fluxes between
two successive nights, we find that for EPIC 204638512 and EPIC 205151387, we
find that the properties of the dust differ from that seen in the diffuse
interstellar medium and denser molecular clouds. However, the grain properties
needed to explain the extinction does resemble those used to model the disks of
many young stellar objects. The wavelength-dependent extinction models of both
EPIC 204638512 and EPIC 205151387 includes grains at least 500 microns in size,
but lacks grains smaller than 0.25 microns. The change in extinction during the
dips, and the timescale for these variations to occur, imply obscuration by the
surface layers of the inner disks. The recent discovery of a highly
mis-inclined inner disk in EPIC 204638512 is suggests that the variations in
this disk system may point to due to rapid changes in obscuration by the
surface layers of its inner disk, and that other face-on Dippers might have
similar geometries. The He I line at 1.083 microns in EPIC 205151387 and EPIC
20463851 were seen to change from night to night, suggesting that we are seeing
He I gas mixed in with the surface dust.Comment: 13 pages, 6 figures, 2 table
Variability of Disk Emission in Pre-Main Sequence and Related Stars IV. Investigating the Structural Changes in the Inner Disk Region of MWC 480
We present five epochs of near IR observations of the protoplanetary disk
around MWC 480 (HD31648) obtained with the SpeX spectrograph on NASA's Infrared
Telescope Facility (IRTF) between 2007 and 2013, inclusive. Using the measured
line fluxes in the Pa beta and Br gamma lines, we found the mass accretion
rates to be (1.43 - 2.61)x10^-8 Msun y^-1 and (1.81 - 2.41)x10^-8 Msun y^-1
respectively, but which varied by more than 50% from epoch to epoch. The
spectral energy distribution (SED)reveals a variability of about 30% between
1.5 and 10 microns during this same period of time. We investigated the
variability using of the continuum emission of the disk in using the
Monte-Carlo Radiative Transfer Code (MCRT) HOCHUNK3D. We find that varying the
height of the inner rim successfully produces a change in the NIR flux, but
lowers the far IR emission to levels below all measured fluxes. Because the
star exhibits bipolar flows, we utilized a structure that simulates an inner
disk wind to model the variability in the near IR, without producing flux
levels in the far IR that are inconsistent with existing data. For this object,
variable near IR emission due to such an outflow is more consistent with the
data than changing the scale height of the inner rim of the disk.Comment: 19 pages, 14 figure
Direct images and spectroscopy of a giant protoplanet driving spiral arms in MWC 758
Understanding the driving forces behind spiral arms in protoplanetary disks
remains a challenge due to the faintness of young giant planets. MWC 758 hosts
such a protoplanetary disk with a two-armed spiral pattern that is suggested to
be driven by an external giant planet. We present new thermal infrared
observations that are uniquely sensitive to redder (i.e., colder or more
attenuated) planets than past observations at shorter wavelengths. We detect a
giant protoplanet, MWC 758c, at a projected separation of ~100 au from the
star. The spectrum of MWC 758c is distinct from the rest of the disk and
consistent with emission from a planetary atmosphere with Teff = 500 +/- 100 K
for a low level of extinction (AV<30), or a hotter object with a higher level
of extinction. Both scenarios are commensurate with the predicted properties of
the companion responsible for driving the spiral arms. MWC 758c provides
evidence that spiral arms in protoplanetary disks can be caused by cold giant
planets or by those whose optical emission is highly attenuated. MWC 758c
stands out both as one of the youngest giant planets known, and also as one of
the coldest and/or most attenuated. Furthermore, MWC 758c is among the first
planets to be observed within a system hosting a protoplanetary disk.Comment: Published in Nature Astronom
Wavelength-dependent Extinction and Grain Sizes in âDippersâ
We have examined internight variability of K2-discovered âdippersâ that are not close to being viewed edge-on, as determined from previously reported ALMA images, using the SpeX spectrograph on NASAâs Infrared Telescope Facility. The three objects observed were EPIC 203850058, EPIC 205151387, and EPIC 204638512 (=2MASS J16042165-2130284). Using the ratio of the fluxes between two successive nights, we find that for EPIC 204638512 and EPIC 205151387, we find that the properties of the dust differ from that seen in the diffuse interstellar medium and denser molecular clouds. However, the grain properties needed to explain the extinction does resemble those used to model the disks of many young stellar objects. The wavelength-dependent extinction models of both EPIC 204638512 and EPIC 205151387 includes grains at least 500 ÎŒ m in size, but lacks grains smaller than 0.25 ÎŒ m. The change in extinction during the dips, and the timescale for these variations to occur, imply obscuration by the surface layers of the inner disks. The recent discovery of a highly misinclined inner disk in EPIC 204638512 is suggests that the variations in this disk system may point to due to rapid changes in obscuration by the surface layers of its inner disk, and that other âface-onâ dippers might have similar geometries. The He i line at 1.083 ÎŒ m in EPIC 205151387 and EPIC 20463851 were seen to change from night to night, suggesting that we are seeing He i gas mixed in with the surface dust
Direct images and spectroscopy of a giant protoplanet driving spiral arms in MWC 758
Understanding the driving forces behind spiral arms in protoplanetary disks remains a challenge due to the faintness of young giant planets. MWC 758 hosts such a protoplanetary disk with a two-armed spiral pattern that is suggested to be driven by an external giant planet. We present observations in the thermal infrared that are uniquely sensitive to redder (that is, colder, or more attenuated) planets than past observations at shorter wavelengths. We detect a giant protoplanet, MWC 758c, at a projected separation of roughly 100 au from the star. The spectrum of MWC 758c is distinct from the rest of the disk and consistent with emission from a planetary atmosphere with T eff = 500 ± 100 K for a low level of extinction (A V †30), or a hotter object with a higher level of extinction. Both scenarios are commensurate with the predicted properties of the companion responsible for driving the spiral arms. MWC 758c provides evidence that spiral arms in protoplanetary disks can be caused by cold giant planets or by those whose optical emission is highly attenuated. MWC 758c stands out both as one of the youngest giant planets known, and as one of the coldest and/or most attenuated. Furthermore, MWC 758c is among the first planets to be observed within a system hosting a protoplanetary disk.6 month embargo; first published 06 July 2023This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]