The Ages of a-Stars. I. Interferometric Observations and Age Estimates for Stars in the Ursa Major Moving Group

Jones, Jeremy; White, R. J.; Boyajian, Tabetha S.; Schaefer, Gail H.; Baines, Ellyn K.; Ireland, Michael; Patience, Jennifer; Brummelaar, T. ten; McAlister, Harold A.; Ridgway, Stephen T.; Sturmann, J.; Sturmann, L.; Turner, N.; Farrington, C.; Goldfinger, P. J.

doi:10.1088/0004-637x/813/1/58

Cited by 60 publications

(43 citation statements)

References 62 publications

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“…Allers & Liu (2013a) find this object's near-IR spectrum is consistent in gravity with field objects. King et al (2003) and Jones et al (2015) estimate ages for the Ursa Major core members of 500 ± 100 Myr and 414 ± 23 Myr, respectively, consistent with the spectroscopic gravity. The absolute magnitudes of DENIS J1705−0516 are also consistent with field objects, so its spectrophotometry and kinematics are in accord.…”

Section: Mass J14112131−2119503 (M9/m8 Int-g)supporting

confidence: 60%

“…Our remaining objects were flagged by Seifahrt et al (2010) as candidates of the nearby moving groups studied by Montes et al (2001): the Pleiades (1 object; 130±20 Myr [Barrado y Navascués et al 2004]), Ursa Majoris (2 objects; ≈400-500 Myr Jones et al 2015]), and Hyades (4 objects; ≈600-800 Myr) moving groups. Note that these are not the open clusters themselves, but rather more dispersed stars claimed to be coeval with the clusters.…”

Section: Samplementioning

confidence: 99%

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The Hawaii Infrared Parallax Program. Ii. Young Ultracool Field Dwarfs* †

Liu

Dupuy

Allers

2016

ApJ

241

320

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We present a large, uniform analysis of young (≈10-150 Myr) ultracool dwarfs, based on new high-precision infrared (IR) parallaxes for 68 objects. We find that low-gravity (vl-g) late-M and L dwarfs form a continuous sequence in IR color-magnitude diagrams, separate from the field population and from current theoretical models. These vl-g objects also appear distinct from young substellar (brown dwarf and exoplanet) companions, suggesting the two populations may have a different range of physical properties. In contrast, at the L/T transition, young, old, and spectrally peculiar objects all span a relatively narrow range in near-IR absolute magnitudes. At a given spectral type, the IR absolute magnitudes of young objects can be offset from ordinary field dwarfs, with the largest offsets occurring in the Y and J bands for late-M dwarfs (brighter than the field) and mid/late-L dwarfs (fainter than the field). Overall, low-gravity (vl-g) objects have the most uniform photometric behavior while intermediate-gravity (int-g) objects are more diverse, suggesting a third governing parameter beyond spectral type 1 This work is largely based on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, and the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.2 Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. -2 -and gravity class. We examine the moving group membership for all young ultracool dwarfs with parallaxes, changing the status of 23 objects (including 8 previously identified planetary-mass candidates) and fortifying the status of another 28 objects. We use our resulting age-calibrated sample to establish empirical young isochrones and show a declining frequency of vl-g objects relative to int-g objects with increasing age. Notable individual objects in our sample include high-velocity ( 100 km s −1 ) int-g objects; very red late-L dwarfs with high surface gravities; candidate disk-bearing members of the MBM20 cloud and β Pic moving group; and very young distant interlopers. Finally, we provide a comprehensive summary of the absolute magnitudes and spectral classifications of young ultracool dwarfs, using a combined sample of 102 objects found in the field and as substellar companions to young stars.Subject headings: brown dwarfs -proper motions -parallaxes -solar neighborhood IntroductionObservational studies of brown dwarfs have been inspired by two complementary perspectives. One has been the desire to expand the parameter space of classical stellar astrophysics. Brown dwarfs are t...

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Section: Mass J14112131−2119503 (M9/m8 Int-g)supporting

confidence: 60%

Section: Samplementioning

confidence: 99%

The Hawaii Infrared Parallax Program. Ii. Young Ultracool Field Dwarfs* †

Liu

Dupuy

Allers

2016

ApJ

241

320

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“…The highest potential of finding a truly habitable planet may lie with K stars. Myr, Bell et al 2015), Ursa Majoris (414 ± 23 Myr; Jones et al 2015Jones et al , 2017, Praesepe (600 Myr, Hillenbrand 2007), andHyades (625 ± 50 Myr, Perryman et al 1997). In addition, we define a field star sample as K stars within 30 pc to which we assign an Figure 3.…”

Section: The K Star Advantagementioning

confidence: 99%

HAZMAT. V. The Ultraviolet and X-Ray Evolution of K Stars

Richey-Yowell

Shkolnik

Schneider

et al. 2019

ApJ

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Knowing the high-energy radiation environment of a star over a planet's formation and evolutionary period is critical in determining if that planet is potentially habitable and if any biosignatures could be detected, as UV radiation can severely change or destroy a planet's atmosphere. Current efforts for finding a potentially habitable planet are focused on M stars, yet K stars may offer more habitable conditions due to decreased stellar activity and more distant and wider habitable zones (HZ). While M star activity evolution has been observed photometrically and spectroscopically, there has been no dedicated investigation of K-star UV evolution. We present the first comprehensive study of the near-UV, far-UV, and X-ray evolution of K stars. We used members of young moving groups and clusters ranging in age from 10 -625 Myr combined with field stars and their archived GALEX UV and ROSAT X-ray data to determine how the UV and X-ray radiation evolve. We find that the UV and X-ray flux incident on a HZ planet is 5 -50 times lower than that of HZ planets around early-M stars and 50 -1000 times lower than those around late-M stars, due to both an intrinsic decrease in K dwarf stellar activity occurring earlier than for M dwarfs and the more distant location of the K dwarf HZ.

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“…King et al 2003;King & Schuler 2005;Brandt & Huang 2015). Jones et al (2015) use interferometric measurements and modelling of A type stars in Ursa Major to determine a more precise and consistent age of 414 ± 23 Myr. Nevertheless, the X-ray and UV emissions from J1036 imply signs of youth by showing similar trends as other low-mass stars of comparable spectral type in the UMa MG (e.g.…”

Section: Age Distance and Group Membershipmentioning

confidence: 99%

The discrepancy between dynamical and theoretical mass in the triplet-system 2MASS J10364483+1521394

Calissendorff

Janson

Köhler

et al. 2017

A&A

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We combine new Lucky Imaging astrometry from NTT/AstraLux Sur with already published astrometry from the AstraLux Large M-dwarf Multiplicity Survey to compute orbital elements and individual masses of the 2MASS J10364483+1521394 triple system belonging to the Ursa-Major moving group. The system consists of one primary low-mass M-dwarf orbited by two less massive companions, for which we determine a combined dynamical mass of M B+C = 0.48 ± 0.14 M . We show from the companions relative motions that they are of equal mass (with a mass ratio of 1.00±0.03), thus 0.24±0.07 M individually, with a separation of 3.2±0.3 AU and conclude that these masses are significantly higher (30%) than what is predicted by theoretical stellar evolutionary models. The biggest uncertainty remains the distance to the system, here adopted as 20.1±2.0 pc based on trigonometric parallax, whose ambiguity has a major impact on the result. With the new observational data we are able to conclude that the orbital period of the BC pair is 8.41 +0.04 −0.02 years.

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The Ages of a-Stars. I. Interferometric Observations and Age Estimates for Stars in the Ursa Major Moving Group

Cited by 60 publications

References 62 publications

The Hawaii Infrared Parallax Program. Ii. Young Ultracool Field Dwarfs* †

The Hawaii Infrared Parallax Program. Ii. Young Ultracool Field Dwarfs* †

HAZMAT. V. The Ultraviolet and X-Ray Evolution of K Stars

The discrepancy between dynamical and theoretical mass in the triplet-system 2MASS J10364483+1521394

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