skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Retrieving the C and O Abundances of HR 7672 AB: A Solar-type Primary Star with a Benchmark Brown Dwarf
Abstract A benchmark brown dwarf (BD) is a BD whose properties (e.g., mass and chemical composition) are precisely and independently measured. Benchmark BDs are valuable in testing theoretical evolutionary tracks, spectral synthesis, and atmospheric retrievals for substellar objects. Here, we report results of atmospheric retrieval on a synthetic spectrum and a benchmark BD, HR 7672 B, with petitRADTRANS . First, we test the retrieval framework on a synthetic PHOENIX BT-Settl spectrum with a solar composition. We show that the retrieved C and O abundances are consistent with solar values, but the retrieved C/O is overestimated by 0.13–0.18, which is about four times higher than the formal error bar. Second, we perform retrieval on HR 7672 B using high spectral-resolution data ( R = 35,000) from the Keck Planet Imager and Characterizer and near-infrared photometry. We retrieve [C/H], [O/H], and C/O to be −0.24 ± 0.05, −0.19 ± 0.04, and 0.52 ± 0.02. These values are consistent with those of HR 7672 A within 1.5 σ . As such, HR 7672 B is among only a few benchmark BDs (along with Gl 570 D and HD 3651 B) that have been demonstrated to have consistent elemental abundances with their primary stars. Our work provides a practical procedure of testing and performing atmospheric retrieval, and sheds light on potential systematics of future retrievals using high- and low-resolution data.  more » « less
Award ID(s):
2143400
PAR ID:
10399534
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more » ; ; ; ; ; ; ; ; ; ; ; ; ; « less
Date Published:
Journal Name:
The Astronomical Journal
Volume:
163
Issue:
4
ISSN:
0004-6256
Page Range / eLocation ID:
189
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, The Astrophysical Journal)
    Abstract Direct imaging studies have mainly used low-resolution spectroscopy ( R ∼ 20–100) to study the atmospheres of giant exoplanets and brown dwarf companions, but the presence of clouds has often led to degeneracies in the retrieved atmospheric abundances (e.g., carbon-to-oxygen ratio, metallicity). This precludes clear insights into the formation mechanisms of these companions. The Keck Planet Imager and Characterizer (KPIC) uses adaptive optics and single-mode fibers to transport light into NIRSPEC ( R ∼ 35,000 in the K band), and aims to address these challenges with high-resolution spectroscopy. Using an atmospheric retrieval framework based on petitRADTRANS , we analyze the KPIC high-resolution spectrum (2.29–2.49 μ m) and the archival low-resolution spectrum (1–2.2 μ m) of the benchmark brown dwarf HD 4747 B ( m = 67.2 ± 1.8 M Jup , a = 10.0 ± 0.2 au, T eff ≈ 1400 K). We find that our measured C/O and metallicity for the companion from the KPIC high-resolution spectrum agree with those of its host star within 1 σ –2 σ . The retrieved parameters from the K -band high-resolution spectrum are also independent of our choice of cloud model. In contrast, the retrieved parameters from the low-resolution spectrum are highly sensitive to our chosen cloud model. Finally, we detect CO, H 2 O, and CH 4 (volume-mixing ratio of log(CH 4 ) = −4.82 ± 0.23) in this L/T transition companion with the KPIC data. The relative molecular abundances allow us to constrain the degree of chemical disequilibrium in the atmosphere of HD 4747 B, and infer a vertical diffusion coefficient that is at the upper limit predicted from mixing length theory. 
    more » « less
  2. ; ; ; (, The Astrophysical Journal)
    Abstract Brown dwarf spectra offer vital testbeds for our understanding of the chemical and physical processes that sculpt substellar atmospheres. Recently, atmospheric retrieval approaches have been successfully applied to low-resolution (R∼ 100) spectra of L, T, and Y dwarfs, yielding constraints on the chemical abundances and temperature structures of these atmospheres. Medium-resolution (R∼ 103) spectra of brown dwarfs offer additional insight, as molecular features are more easily disentangled and the thermal structure of the upper atmosphere is better probed. We present results from a GPU-based retrieval analysis of a high signal-to-noise, medium-resolution (R∼ 6000) FIRE spectrum from 0.85 to 2.5μm of the T9 dwarf UGPS J072227.51–054031.2. At 60× higher spectral resolution than previous brown dwarf retrievals, a number of novel challenges arise. We examine the effect of different opacity sources, in particular for CH4. Furthermore, we find that flaws in the data like errors from order stitching can bias our constraints. We compare these retrieval results to those for anR∼ 100 spectrum of the same object, revealing how constraints on atmospheric abundances and temperatures improve by an order of magnitude or more with increased spectral resolution. In particular, we can constrain the abundance of H2S, which is undetectable at lower spectral resolution. While these medium-resolution retrievals offer the potential of precise, stellar-like constraints on atmospheric abundances (∼0.02 dex), our retrieved radius is unphysically small ( R = 0.50 − 0.01 + 0.01 RJup), indicating shortcomings with our modeling framework. This work is an initial investigation into brown dwarf retrievals at medium spectral resolution, offering guidance for future ground-based studies and JWST observations. 
    more » « less
  3. ; ; ; ; ; ; ; ; (, The Astrophysical Journal)
    Abstract We present results from an atmospheric retrieval analysis of Gl 229B using the Brewster retrieval code. We find the best fit model to be cloud-free, consistent with the T dwarf retrieval work of Line et al.; Zalesky et al. and Gonzales et al. Fundamental parameters (mass, radius, log(LBol/LSun), log(g)) determined from our model agree within 1σto SED-derived values, except forTeffwhere our retrievedTeffis approximately 100 K cooler than the evolutionary model-based SED value. We find a retrieved mass of 50 − 9 + 12 MJup, however, we also find that the observables of Gl 229B can be explained by a cloud-free model with a prior on mass at the dynamical value, 70MJup. We are able to constrain abundances for H2O, CO, CH4, NH3, Na and K and find a supersolar C/O ratio as compared to its primary, Gl 229A. We report an overall subsolar metallicity due to atmospheric oxygen depletion, but find a solar [C/H], which matches that of the primary. We find that this work contributes to a growing trend in retrieval-based studies, particularly for brown dwarfs, toward supersolar C/O ratios and discuss the implications of this result on formation mechanisms and internal physical processes, as well as model biases. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, The Astronomical Journal)
    Abstract Measurements of the carbon-to-oxygen (C/O) ratios of exoplanet atmospheres can reveal details about their formation and evolution. Recently, high-resolution cross-correlation analysis has emerged as a method of precisely constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultrahot Jupiter WASP-76b observed between 1.4 and 2.4μm with the high-resolution Immersion GRating INfrared Spectrometer on the Gemini-S telescope. We detected the presence of H2O, CO, and OH at signal-to-noise ratios of 6.93, 6.47, and 3.90, respectively. We performed two retrievals on this data set. A free retrieval for abundances of these three species retrieved a volatile metallicity of C + O H = − 0.70 − 0.93 + 1.27 , consistent with the stellar value, and a supersolar carbon-to-oxygen ratio of C/O = 0.80 − 0.11 + 0.07 . We also ran a chemically self-consistent grid retrieval, which agreed with the free retrieval within 1σbut favored a slightly more substellar metallicity and solar C/O ratio ( C + O H = − 0.74 − 0.17 + 0.23 and C/O = 0.59 − 0.14 + 0.13 ). A variety of formation pathways may explain the composition of WASP-76b. Additionally, we found systemic (Vsys) and Keplerian (Kp) velocity offsets which were broadly consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshiftedVsysfor H2O. Future observations to measure the phase-dependent velocity offsets and limb differences at high resolution on WASP-76b will be necessary to understand the H2O velocity shift. Finally, we find that the population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios. More results from high-resolution observations or JWST will serve to further elucidate any population-level trends. 
    more » « less
  5. (, The Astronomical Journal)
    Abstract Half of the JWST high-contrast imaging objects will only have photometric data as of Cycle 2. However, to better understand their atmospheric chemistry that informs formation origin, spectroscopic data are preferred. Using HIP 65426 b, we investigate to what extent planet properties and atmospheric chemical abundance can be retrieved with only JWST photometric data points (2.5–15.5μm) in conjunction with ground-based archival low-resolution spectral data (1.0–2.3μm). We find that the data is consistent with an atmosphere with solar metallicity and C/O ratios at 0.40 and 0.55. We rule out 10× solar metallicity and an atmosphere with C/O = 1.0. We also find strong evidence of silicate clouds but no sign of an enshrouding featureless dust extinction. This work offers guidance and cautionary tales on analyzing data in the absence of medium-to-high-resolution spectral data. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email