分类： 天文学 >> 天文学 提交时间： 2023-02-19
Sukanya Chakrabarti
Joshua D. Simon
Peter A. Craig
Henrique Reggiani
Puragra Guhathakurta
Paul A. Dalba
Evan N. Kirby
Philip Chang
Daniel R. Hey
Alessandro Savino
Marla Geha
摘要： We describe the discovery of a solar neighborhood ($d=474$~pc) binary system consisting of a main-sequence sunlike star and a massive non-interacting black hole candidate. We selected this system from the \textit{Gaia} DR3 binary catalog based on its high mass ratio and location close to the main sequence. The spectral energy distribution (SED) of the visible star is well described by a single stellar model, indicating that no contribution from another luminous source is needed to fit the observed photometry. We derive stellar parameters from a high S/N Magellan/MIKE spectrum, classifying the star as a main-sequence star with $T_{\rm eff} = 5972~\rm K$, $\log{g} = 4.54$, and $M = 0.91$~\msun. The spectrum also shows no indication of a second luminous component. We have measured radial velocities of this system with the Automated Planet Finder, Magellan, and Keck over the past three months, which we use to determine the spectroscopic orbit of the binary. We show that the velocity data are consistent with the \textit{Gaia} astrometric orbit and provide independent evidence for a massive dark companion. From a combined fit of the astrometric and spectroscopic data, we derive a companion mass of $11.9^{+2.0}_{-1.6}$\msun. We conclude that this binary system harbors a massive black hole on an eccentric $(e =0.45 \pm 0.02)$, long-period ($185.4 \pm 0.1$ d) orbit. The main-sequence star that orbits this black hole is moderately metal-poor ($\mbox{[Fe/H]} = -0.30$), on a Galactic orbit similar to thin disk stars. Our conclusions are independent of \cite{ElBadry2022Disc}, who recently reported the discovery of the same system, and find a marginally lower companion mass than we do here.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Alexandra Z. Greenbaum
Jorge Llop-Sayson
Ben Lew
Geoffrey Bryden
Thomas Roellig
Marie Ygouf
B. J. Fulton
Daniel R. Hey
Daniel Huber
Sagnick Mukherjee
Michael Meyer
Jarron Leisenring
Marcia Rieke
Martha Boyer
Joseph J. Green
Doug Kelly
Karl Misselt
Eugene Serabyn
John Stansberry
Laurie E. U. Chu
摘要： We observed HD 19467 B with JWST's NIRCam in six filters spanning 2.5-4.6 $\mu m$ 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 $\sim1000$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 $2\times10^{-4}$ to $2\times10^{-5}$) 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 9.4$\pm$0.9 Gyr inferred from spectroscopy, Gaia astrometry, and TESS asteroseismology, we obtain a model-derived mass of 62$\pm 1M_{J}$, which is consistent within 2-$\sigma$ with the dynamically derived mass of 81$^{+14}_{-12}M_{J}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Timothy R. Bedding
Simon J. Murphy
Courtney Crawford
Daniel R. Hey
Daniel Huber
Hans Kjeldsen
Yaguang Li
Andrew W. Mann
Guillermo Torres
Timothy R. White
George Zhou
摘要： We studied 89 A- and F-type members of the Pleiades open cluster, including five escaped members. We measured projected rotational velocities (v sin i) for 49 stars and confirmed that stellar rotation causes a broadening of the main sequence in the color-magnitude diagram. Using time-series photometry from NASA's TESS Mission (plus one star observed by Kepler/K2), we detected delta Scuti pulsations in 36 stars. The fraction of Pleiades stars in the middle of the instability strip that pulsate is unusually high (over 80%), and their range of effective temperatures agrees well with theoretical models. On the other hand, the characteristics of the pulsation spectra are varied and do not correlate with stellar temperature, calling into question the existence of a useful nu_max relation for delta Scutis, at least for young stars. By including delta Scuti stars observed in the Kepler field, we show that the instability strip is shifted to the red with increasing distance by interstellar reddening. Overall, this work demonstrates the power of combining observations with Gaia and TESS for studying pulsating stars in open clusters.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yaguang Li
Timothy R. Bedding
Simon J. Murphy
Dennis Stello
Yifan Chen
Daniel Huber
Meridith Joyce
Dion Marks
Xianfei Zhang
Shaolan Bi
Isabel L. Colman
Michael R. Hayden
Daniel R. Hey
Gang Li
Benjamin T. Montet
Sanjib Sharma
Yaqian Wu
摘要： A star expands to become a red giant when it has fused all the hydrogen in its core into helium. If the star is in a binary system, its envelope can overflow onto its companion or be ejected into space, leaving a hot core and potentially forming a subdwarf-B star. However, most red giants that have partially transferred envelopes in this way remain cool on the surface and are almost indistinguishable from those that have not. Among $\sim$7000 helium-burning red giants observed by NASA's Kepler mission, we use asteroseismology to identify two classes of stars that must have undergone dramatic mass loss, presumably due to stripping in binary interactions. The first class comprises about 7 underluminous stars with smaller helium-burning cores than their single-star counterparts. Theoretical models show that these small cores imply the stars had much larger masses when ascending the red giant branch. The second class consists of 32 red giants with masses down to 0.5 M$_\odot$, whose implied ages would exceed the age of the universe had no mass loss occurred. The numbers are consistent with binary statistics, and our results open up new possibilities to study the evolution of post-mass-transfer binary systems.
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