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Jones, H. R. A.

Publications and source records attributed to Jones, H. R. A..

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Primeval very low-mass stars and brown dwarfs – VIII. The first age benchmark L subdwarf, a wide companion to a halo white dwarf

ABSTRACT We report the discovery of five white dwarf + ultracool dwarf systems identified as common proper motion wide binaries in the Gaia Catalogue of Nearby Stars. The discoveries include a white dwarf + L subdwarf binary, VVV 1256−62AB, a gravitationally bound system located 75.6$^{+1.9}_{-1.8}$ pc away with a projected separation of 1375$^{+35}_{-33}$ au. The primary is a cool DC white dwarf with a hydrogen dominated atmosphere, and has a total age of $10.5^{+3.3}_{-2.1}$ Gyr, based on white dwarf model fitting. The secondary is an L subdwarf with a metallicity of [M/H] = $-0.72^{+0.08}_{-0.10}$ (i.e. [Fe/H] = $-0.81\pm 0.10$) and $T_{\rm eff}$ = 2298$^{+45}_{-43}$ K based on atmospheric model fitting of its optical to near infrared spectrum, and likely has a mass just above the stellar/substellar boundary. The subsolar metallicity of the L subdwarf and the system’s total space velocity of 406 km s−1 indicates membership in the Galactic halo, and it has a flat eccentric Galactic orbit passing within 1 kpc of the centre of the Milky Way every $\sim$0.4 Gyr and extending to 15–31 kpc at apogal. VVV 1256−62B is the first L subdwarf to have a well-constrained age, making it an ideal benchmark of metal-poor ultracool dwarf atmospheres and evolution.

Zhang, Z. H. (ORCID:000000033047607X)↗
DOE OSTI2015

Starspot distributions on fully convective M dwarfs: Implications for radial velocity planet searches

Since M4.5–M9 dwarfs exhibit equatorial rotation velocities of the order of 10 km s{sup −1} on average, radial velocity surveys targeting this stellar population will likely need to find methods to effectively remove starspot jitter. We present the first high resolution Doppler images of the M4.5 dwarf, GJ 791.2A, and the M9 dwarf, LP 944-20. The time series spectra of both objects reveal numerous line profile distortions over the rotation period of each star, which we interpret as starspots. The transient distortions are modeled with spot/photosphere contrast ratios that correspond to model atmosphere temperature differences of T{sub phot}−T{sub spot} = 300 and 200 K. GJ 791.2A is a fully convective star with v sin i = 35.1 km s{sup −1}. Although we find more starspot structure at high latitudes, we reconstruct spots at a range of phases and latitudes with a mean spot filling of ∼3%. LP 944-20 is one of the brightest known late-M dwarfs, with spectral type M9V and v sin i = 30.8 km s{sup −1}. Its spectral time series exhibits two dominant transient line distortions that are reconstructed as high latitude spots, while a mean spot filling factor of only 1.5% is found. The occurrence of low-contrast spots at predominantly high latitudes, which we see in both targets here, is, in general, likely to be responsible for the low amplitude photometric variability seen in late-M dwarfs. For GJ 791.2A, the radial velocities induced by the starspot features yield an rms velocity variability of 138 m s{sup −1}, which can be reduced by a factor of 1.9 using our reconstructed surface brightness distributions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Gj 832c: A super-Earth in the habitable zone

We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly circular 9.4 yr orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35.68 ± 0.03 days and minimum mass (m sin i) of 5.4 ± 1.0 Earth masses. GJ 832c moves on a low-eccentricity orbit (e = 0.18 ± 0.13) toward the inner edge of the habitable zone. However, given the large mass of the planet, it seems likely that it would possess a massive atmosphere, which may well render the planet inhospitable. Indeed, it is perhaps more likely that GJ 832c is a 'super-Venus', featuring significant greenhouse forcing. With an outer giant planet and an interior, potentially rocky planet, the GJ 832 planetary system can be thought of as a miniature version of our own solar system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The anglo-australian planet search. XXIII. Two new Jupiter analogs

We report the discovery of two long-period giant planets from the Anglo-Australian Planet Search. HD 154857c is in a multiple-planet system, while HD 114613b appears to be solitary. HD 114613b has an orbital period P = 10.5 yr, and a minimum mass msin i of 0.48 M {sub Jup}; HD 154857c has P = 9.5 yr and msin i = 2.6 M {sub Jup}. These new data confirm the planetary nature of the previously unconstrained long-period object in the HD 154857 system. We have performed detailed dynamical stability simulations which show that the HD 154857 two-planet system is stable on timescales of at least 10{sup 8} yr. These results highlight the continued importance of 'legacy' surveys with long observational baselines; these ongoing campaigns are critical for determining the population of Jupiter analogs, and hence of those planetary systems with architectures most like our own solar system.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A detailed analysis of the HD 73526 2:1 resonant planetary system

We present six years of new radial velocity data from the Anglo-Australian and Magellan Telescopes on the HD 73526 2:1 resonant planetary system. We investigate both Keplerian and dynamical (interacting) fits to these data, yielding four possible configurations for the system. The new data now show that both resonance angles are librating, with amplitudes of 40° and 60°, respectively. We then perform long-term dynamical stability tests to differentiate these solutions, which only differ significantly in the masses of the planets. We show that while there is no clearly preferred system inclination, the dynamical fit with i = 90° provides the best combination of goodness-of-fit and long-term dynamical stability.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Parallaxes of southern extremely cool objects (parsec). II. Spectroscopic follow-up and parallaxes of 52 targets

We present near-infrared spectroscopy for 52 ultracool dwarfs, including two newly discovered late-M dwarfs, one new late-M subdwarf candidate, three new L, and four new T dwarfs. We also present parallaxes and proper motions for 21 of them. Four of the targets presented here have previous parallax measurements, while all the others are new values. This allow us to populate further the spectral sequence at early types (L0-L4). Combining the astrometric parameters with the new near-infrared spectroscopy presented here, we are able to investigate further the nature of some of the objects. In particular, we find that the peculiar blue L1 dwarf SDSS J133148.92–011651.4 is a metal-poor object, likely a member of the galactic thick disk. We discover a new M subdwarf candidate, 2MASS J20115649–6201127. We confirm the low-gravity nature of EROS-MP J0032–4405, DENIS-P J035726.9–441730, and 2MASS J22134491–2136079. We present two new metal-poor dwarfs: the L4pec 2MASS J19285196–4356256 and the M7pec SIPS2346–5928. We also determine the effective temperature and bolometric luminosity of the 21 targets with astrometric measurements, and we obtain a new polynomial relation between effective temperature and near-infrared spectral type. The new fit suggests a flattening of the sequence at the transition between M and L spectral types. This could be an effect of dust formation, which causes a more rapid evolution of the spectral features as a function of the effective temperature.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

FOREVER ALONE? TESTING SINGLE ECCENTRIC PLANETARY SYSTEMS FOR MULTIPLE COMPANIONS

Determining the orbital eccentricity of an extrasolar planet is critically important for understanding the system's dynamical environment and history. However, eccentricity is often poorly determined or entirely mischaracterized due to poor observational sampling, low signal-to-noise, and/or degeneracies with other planetary signals. Some systems previously thought to contain a single, moderate-eccentricity planet have been shown, after further monitoring, to host two planets on nearly circular orbits. We investigate published apparent single-planet systems to see if the available data can be better fit by two lower-eccentricity planets. We identify nine promising candidate systems and perform detailed dynamical tests to confirm the stability of the potential new multiple-planet systems. Finally, we compare the expected orbits of the single- and double-planet scenarios to better inform future observations of these interesting systems.

79 ASTRONOMY AND ASTROPHYSICS↗