18 research outputs found
Predicting Cloud Conditions in Substellar Mass Objects Using Ultracool Dwarf Companions
© 2024 The Author(s). Published by the American Astronomical Society. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/We present results from conducting a theoretical chemical analysis of a sample of benchmark companion brown dwarfs whose primary star is of type F, G or K. We summarize the entire known sample of these types of companion systems, termed "compositional benchmarks", that are present in the literature or recently published as key systems of study in order to best understand brown dwarf chemistry and condensate formation. Via mass balance and stoichiometric calculations, we predict a median brown dwarf atmospheric oxygen sink of by utilizing published stellar abundances in the local solar neighborhood. Additionally, we predict a silicate condensation sequence such that atmospheres with bulk Mg/Si 0.9 will form enstatite (MgSiO) and quartz (SiO) clouds and atmospheres with bulk Mg/Si 0.9 will form enstatite and forsterite (MgSiO) clouds. Implications of these results on C/O ratio trends in substellar mass objects and utility of these predictions in future modeling work are discussed.Peer reviewe
Discovery of a Mid-L Dwarf Companion to the L 262-74 System
We present the discovery of CWISE J151044.74524923.5, a wide low-mass
companion to the nearby (24.7 pc) system L 262-74, which was identified
through the Backyard Worlds: Planet 9 citizen science project. We detail the
properties of the system, and we assess that this companion is a mid-L dwarf,
which will need to be verified spectroscopically. With an angular separation of
74\farcs3, we estimate a projected physical separation of 1837 au from
the central system
WISEA J083011.95+283716.0: A Missing Link Planetary-mass Object
We present the discovery of WISEA J083011.95+283716.0, the first Y-dwarf candidate identified through the "Backyard Worlds: Planet 9" citizen science project. We identified this object as a red, fast-moving source with a faint W2 detection in multiepoch AllWISE and unWISE images. We have characterized this object with Spitzer and Hubble Space Telescope's (HST) follow-up imaging. With mid-infrared detections in Spitzer's ch1 and ch2 bands and flux upper limits in HST F105W and F125W filters, we find that this object is both very faint and has extremely red colors (ch1 − ch2 = 3.25 ± 0.23 mag, F125W − ch2 ≥ 9.36 mag), consistent with a T_(eff) ~ 300 K source, as estimated from the known Y-dwarf population. A preliminary parallax provides a distance of 11.1_(-1.5)^(+2.0) pc, leading to a slightly warmer temperature of ~350 K. The extreme faintness and red HST and Spitzer colors of this object suggest that it may be a link between the broader Y-dwarf population and the coldest known brown dwarf WISE J0855−0714, and may highlight our limited knowledge of the true spread of Y-dwarf colors. We also present four additional "Backyard Worlds: Planet 9" late-T brown dwarf discoveries within 30 pc
WISEA J083011.95+283716.0: A Missing Link Planetary-Mass Object
We present the discovery of WISEA J083011.95+283716.0, the first Y dwarf
candidate identified through the Backyard Worlds: Planet 9 citizen science
project. We identified this object as a red, fast-moving source with a faint
detection in multi-epoch \textit{AllWISE} and unWISE images. We have
characterized this object with Spitzer Space Telescope and \textit{Hubble Space
Telescope} follow-up imaging. With mid-infrared detections in
\textit{Spitzer}'s \emph{ch1} and \emph{ch2} bands and flux upper limits in
Hubble Space Telescope and filters, we find that this object is
both very faint and has extremely red colors ( mag,
mag), consistent with a T K source, as
estimated from the known Y dwarf population. A preliminary parallax provides a
distance of pc, leading to a slightly warmer temperature
of K. The extreme faintness and red Hubble Space Telescope and
Spitzer Space Telescope colors of this object suggest it may be a link between
the broader Y dwarf population and the coldest known brown dwarf WISE
J08550714, and highlight our limited knowledge of the true spread of Y dwarf
colors. We also present four additional Backyard Worlds: Planet 9 late-T brown
dwarf discoveries within 30 pc.Comment: 13 pages, 6 figures, 5 table
Methane Emission From a Cool Brown Dwarf
© 2024, The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/Beyond our solar system, aurorae have been inferred from radio obser- vations of isolated brown dwarfs (e.g. [1]; [2]). Within our solar system, giant planets have auroral emission with signatures across the electromag- netic spectrum including infrared emission of H3+ and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features but have only had null detections (e.g. [3]). CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of ∼482 K. Here we report JWST observations of strong methane emission from W1935 at 3.326 microns. Atmospheric mod- eling leads us to conclude that a temperature inversion of ∼300 K centered at 1-10 millibar replicates the feature. This represents an atmospheric tem- perature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and/or external dynamical pro- cesses cannot be ruled out. The best fit model rules out the contribution of H3+ emission which is prominent in solar system gas giants, however this is consistent with rapid destruction of H3+ at the higher pressure where the W1935 emission originates (e.g. [4]).Peer reviewe
WISEA J041451.67–585456.7 and WISEA J181006.18–101000.5: The First Extreme T-type Subdwarfs?
We present the discoveries of WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5, two low-temperature (1200–1400 K), high proper motion T-type subdwarfs. Both objects were discovered via their high proper motion (>0".5 yr⁻¹); WISEA J181006.18−101000.5 as part of the NEOWISE proper motion survey and WISEA J041451.67−585456.7 as part of the citizen science project Backyard Worlds; Planet 9. We have confirmed both as brown dwarfs with follow-up near-infrared spectroscopy. Their spectra and near-infrared colors are unique among known brown dwarfs, with some colors consistent with L-type brown dwarfs and other colors resembling those of the latest-type T dwarfs. While no forward model consistently reproduces the features seen in their near-infrared spectra, the closest matches suggest very low metallicities ([Fe/H] ⩽ −1), making these objects likely the first examples of extreme subdwarfs of the T spectral class (esdT). WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5 are found to be part of a small population of objects that occupy the "substellar transition zone," and have the lowest masses and effective temperatures of all objects in this group
WISEA J041451.67–585456.7 and WISEA J181006.18–101000.5: The First Extreme T-type Subdwarfs?
We present the discoveries of WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5, two low-temperature (1200–1400 K), high proper motion T-type subdwarfs. Both objects were discovered via their high proper motion (>0".5 yr⁻¹); WISEA J181006.18−101000.5 as part of the NEOWISE proper motion survey and WISEA J041451.67−585456.7 as part of the citizen science project Backyard Worlds; Planet 9. We have confirmed both as brown dwarfs with follow-up near-infrared spectroscopy. Their spectra and near-infrared colors are unique among known brown dwarfs, with some colors consistent with L-type brown dwarfs and other colors resembling those of the latest-type T dwarfs. While no forward model consistently reproduces the features seen in their near-infrared spectra, the closest matches suggest very low metallicities ([Fe/H] ⩽ −1), making these objects likely the first examples of extreme subdwarfs of the T spectral class (esdT). WISEA J041451.67−585456.7 and WISEA J181006.18−101000.5 are found to be part of a small population of objects that occupy the "substellar transition zone," and have the lowest masses and effective temperatures of all objects in this group
Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project
We present Spitzer follow-up imaging of 95 candidate extremely cold brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, which uses visually perceived motion in multiepoch Wide-field Infrared Survey Explorer (WISE) images to identify previously unrecognized substellar neighbors to the Sun. We measure Spitzer [3.6]–[4.5] color to phototype our brown dwarf candidates, with an emphasis on pinpointing the coldest and closest Y dwarfs within our sample. The combination of WISE and Spitzer astrometry provides quantitative confirmation of the transverse motion of 75 of our discoveries. Nine of our motion-confirmed objects have best-fit linear motions larger than 1'' yr⁻¹; our fastest-moving discovery is WISEA J155349.96+693355.2 (μ ≈ 2.”15 yr⁻¹), a possible T-type subdwarf. We also report a newly discovered wide-separation (~400 au) T8 comoving companion to the white dwarf LSPM J0055+5948 (the fourth such system to be found), plus a candidate late T companion to the white dwarf LSR J0002+6357 at 5 5 projected separation (~8700 au if associated). Among our motion-confirmed targets, five have Spitzer colors most consistent with spectral type Y. Four of these five have exceptionally red Spitzer colors suggesting types of Y1 or later, adding considerably to the small sample of known objects in this especially valuable low-temperature regime. Our Y dwarf candidates begin bridging the gap between the bulk of the Y dwarf population and the coldest known brown dwarf
Spitzer Follow-up of Extremely Cold Brown Dwarfs Discovered by the Backyard Worlds: Planet 9 Citizen Science Project
We present Spitzer follow-up imaging of 95 candidate extremely cold brown
dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project,
which uses visually perceived motion in multi-epoch WISE images to identify
previously unrecognized substellar neighbors to the Sun. We measure Spitzer
[3.6]-[4.5] color to phototype our brown dwarf candidates, with an emphasis on
pinpointing the coldest and closest Y dwarfs within our sample. The combination
of WISE and Spitzer astrometry provides quantitative confirmation of the
transverse motion of 75 of our discoveries. Nine of our motion-confirmed
objects have best-fit linear motions larger than 1"/yr; our fastest-moving
discovery is WISEA J155349.96+693355.2 (total motion ~2.15"/yr), a possible T
type subdwarf. We also report a newly discovered wide-separation (~400 AU) T8
comoving companion to the white dwarf LSPM J0055+5948 (the fourth such system
to be found), plus a candidate late T companion to the white dwarf LSR
J0002+6357 at 5.5' projected separation (~8,700 AU if associated). Among our
motion-confirmed targets, five have Spitzer colors most consistent with
spectral type Y. Four of these five have exceptionally red Spitzer colors
suggesting types of Y1 or later, adding considerably to the small sample of
known objects in this especially valuable low-temperature regime. Our Y dwarf
candidates begin bridging the gap between the bulk of the Y dwarf population
and the coldest known brown dwarf.Comment: accepted for publication in The Astrophysical Journa