1,721,432 research outputs found
Direct Spectrum of the Benchmark T Dwarf HD 19467 B
Get PDFHD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar-type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R ≈ 30 observations obtained simultaneously across the JH bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5 ± 1 dwarf with effective temperature T_eff=978^(+20)_(-43) K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits
Direct spectrum of the benchmark t dwarf HD 19467 B
No full textHD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar-type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R ≈ 30 observations obtained simultaneously across the JH bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5 ± 1 dwarf with effective temperature Teff = 978+20 -43 K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits
First Observations of the Brown Dwarf HD 19467 B with JWST
Get PDFWe observed HD 19467 B with JWST's NIRCam in six filters spanning 2.5-4.6
with the Long Wavelength Bar coronagraph. The brown dwarf HD 19467 B
was initially identified through a long-period trend in the radial velocity of
G3V star HD 19467. HD 19467 B was subsequently detected via coronagraphic
imaging and spectroscopy, and characterized as a late-T type brown dwarf with
approximate temperature K. We observed HD 19467 B as a part of the
NIRCam GTO science program, demonstrating the first use of the NIRCam Long
Wavelength Bar coronagraphic mask. The object was detected in all 6 filters
(contrast levels of to ) at a separation of
1.6 arcsec using Angular Differential Imaging (ADI) and Synthetic Reference
Differential Imaging (SynRDI). Due to a guidestar failure during acquisition of
a pre-selected reference star, no reference star data was available for
post-processing. However, RDI was successfully applied using synthetic Point
Spread Functions (PSFs) developed from contemporaneous maps of the telescope's
optical configuration. Additional radial velocity data (from Keck/HIRES) are
used to constrain the orbit of HD 19467 B. Photometric data from TESS are used
to constrain the properties of the host star, particularly its age. NIRCam
photometry, spectra and photometry from literature, and improved stellar
parameters are used in conjunction with recent spectral and evolutionary
substellar models to derive physical properties for HD 19467 B. Using an age of
9.40.9 Gyr inferred from spectroscopy, Gaia astrometry, and TESS
asteroseismology, we obtain a model-derived mass of 62, which is
consistent within 2- with the dynamically derived mass of
81.Comment: 21 pages, 19 figures. Accepted to AAS Journal
Benchmarking Substellar Evolutionary Models Using New Age Estimates for HD 4747 B and HD 19467 B
Get PDFConstraining substellar evolutionary models (SSEMs) is particularly difficult due to a degeneracy between the mass, age, and luminosity of a brown dwarf. In cases where a brown dwarf is found as a directly imaged companion to a star, as in HD 4747 and HD 19467, the mass, age, and luminosity of the brown dwarf are determined independently, making them ideal objects to use to benchmark SSEMs. Using the Center for High Angular Resolution Astronomy Array, we measured the angular diameters and calculated the radii of the host stars HD 4747 A and HD 19467 A. After fitting their parameters to the Dartmouth Stellar Evolution Database, MESA Isochrones and Stellar Tracks, and Yonsei-Yale isochronal models, we adopt age estimates of 10.74 -6.75+6.87 Gyr for HD 4747 A and 10.06 -1.16+0.82 Gyr for HD 19467 A. Assuming the brown dwarf companions HD 4747 B and HD 19467 B have the same ages as their host stars, we show that many of the SSEMs under-predict bolometric luminosities by ∼0.75 dex for HD 4747 B and ∼0.5 dex for HD 19467 B. The discrepancies in luminosity correspond to over-predictions of the masses by ∼12% for HD 4747 B and ∼30% for HD 19467 B. We also show that SSEMs that take into account the effect of clouds reduce the under-prediction of luminosity to ∼0.6 dex and the over-prediction of mass to ∼8% for HD 4747 B, an L/T transition object that is cool enough to begin forming clouds. One possible explanation for the remaining discrepancies is missing physics in the models, such as the inclusion of metallicity effects
Direct spectrum of the benchmark t dwarf HD 19467 B
No full textThis is the final version of the article. Available from the American Astronomical Society / IOP Publishing via the DOI in this record.HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar-type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R ≈ 30 observations obtained simultaneously across the JH bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5 ± 1 dwarf with effective temperature Teff = 978+20 -43 K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits.The TrenDS high-contrast imaging program is supported by NASA Origins of Solar Systems grant NNX13AB03G and the NASA Early Career Fellowship program. A portion of this work was supported by the National Science Foundation under Grant Numbers AST-0215793, 0334916, 0520822, 0804417 and 1245018. This work was partially supported by NASA ADAP grant 11-ADAP11-0169 and NSF award AST 1211568. A portion of the research in this Letter was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. J.A. is supported by the National Physical Science Consortium. This research has benefitted from the SpeX Prism Spectral Libraries, maintained by Adam Burgasser.1
Characterizing brown dwarf companions with IRDIS long-slit spectroscopy: HD 1160 B and HD 19467 B
Get PDFInternational audienceThe determination of the fundamental properties (mass, separation, age, gravity, and atmospheric properties) of brown dwarf companions allows us to infer crucial informations on their formation and evolution mechanisms. Spectroscopy of substellar companions is available to date only for a limited number of objects (and mostly at very low resolution, R < 50) because of technical limitations, I.e. contrast and angular resolution. We present medium resolution (R = 350), coronagraphic long-slit spectroscopic observations with SPHERE of two substellar companions, HD 1160 B and HD 19467 B. We found that HD 1160 B has a peculiar spectrum that cannot be fitted by spectra in current spectral libraries. A good fit is possible only considering separately the Y+J and the H spectral band. The spectral type is between M5 and M7. We also estimated a Teff of 2800-2900 K and a log g of 3.5-4.0 dex. The low surface gravity seems to favour young age (10-20 Myr) and low mass (∼20 MJup ) for this object. HD 19467 B is instead a fully evolved object with a Teff of ∼1000 K and log g of ∼5.0 dex. Its spectral type is T6 ± 1
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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