Proper motion and X‐ray selected search for new members of the young TW Hya association

Tachihara, Kengo; Neuhäuser, R.; Frink, S.; Guenther, E. W.

doi:10.1002/asna.200310168

Cited by 5 publications

(6 citation statements)

References 34 publications

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“…HIP 50032 is a moderately active (log R HK = −4.38 Isaacson & Fischer 2010) star with a low lithium abundance (EW(λ6707) = 30 mÅ) compared to pre-main sequence K-type stars (Tachihara et al 2003). Its absolute magnitude (M V = 5.93) calculated using its Hipparcos parallax (van Leeuwen 2007a) is consistent with a main sequence star.…”

Section: A Re-analysis Of Hipparcosmentioning

confidence: 95%

BANYAN. IX. The Initial Mass Function and Planetary-mass Object Space Density of the TW HYA Association

Gagné

Faherty

Mamajek

et al. 2017

ApJS

103

106

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A determination of the initial mass function (IMF) of the current, incomplete census of the 10 Myrold TW Hya association (TWA) is presented. This census is built from a literature compilation supplemented with new spectra and 17 new radial velocities from on-going membership surveys, as well as a re-analysis of Hipparcos data that confirmed HR 4334 (A2 Vn) as a member. Though the dominant uncertainty in the IMF remains census incompleteness, a detailed statistical treatment is carried out to make the IMF determination independent of binning, while accounting for small number statistics. The currently known high-likelihood members are fitted by a log-normal distribution with a central mass of 0.21−0.06 M and a characteristic width of 0.8 +0.2 −0.1 dex in the 12 M Jup -2 M range, whereas a Salpeter power law with α = 2.2 +1.1 −0.5 best describes the IMF slope in the 0.1-2 M range. This characteristic width is higher than other young associations, which may be due to incompleteness in the current census of low-mass TWA stars. A tentative overpopulation of isolated planetary-mass members similar to 2MASS J11472421-2040204 and 2MASS J11193254-1137466 is identified: this indicates that there might be as many as 10 +13 −5 similar members of TWA with hot-start modeldependent masses estimated at ∼ 5-7 M Jup , most of which would be too faint to be detected in 2MASS . Our new radial velocity measurements corroborate the membership of 2MASS J11472421-2040204, and secure TWA 28 (M8.5 γ), TWA 29 (M9.5 γ) and TWA 33 (M4.5 e) as members. The discovery of 2MASS J09553336-0208403, a young L7-type interloper unrelated to TWA, is also presented.

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Section: A Re-analysis Of Hipparcosmentioning

confidence: 95%

BANYAN. IX. The Initial Mass Function and Planetary-mass Object Space Density of the TW HYA Association

Gagné

Faherty

Mamajek

et al. 2017

ApJS

103

106

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show abstract

“…High coronal activity is associated with strong emission lines of atomic hydrogen and large X-ray emission. Spectroscopic follow-up of X-ray sources from the ROSAT catalogs has yielded positive identification of many nearby young stars, including new members of the TW Hydrae association (Tachihara et al 2003) and the β Pictoris moving group (Torres et al 2006). However, the ROSAT catalogs are flux limited, and though they are useful in identifying nearby young stars, they cannot serve as the basis for a complete census of moving group members.…”

Section: Introductionmentioning

confidence: 99%

Nearby Young Stars Selected by Proper Motion. I. Four New Members of the Β Pictoris Moving Group From the Tycho-2 Catalog

Lépine

Simon

2009

The Astronomical Journal

127

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We describe a procedure to identify stars from nearby moving groups and associations out of catalogs of stars with large proper motions. We show that from the mean motion vector of a known or suspected moving group, one can identify additional members of the group based on proper motion data and photometry in the optical and infrared, with minimal contamination from background field stars. We demonstrate this technique by conducting a search for low-mass members of the β Pictoris moving group in the Tycho-2 catalog. All known members of the moving group are easily recovered, and a list of 51 possible candidates is generated. Moving group membership is evaluated for 33 candidates based on X-ray flux from ROSAT , Hα line emission, and radial velocity measurement from high-resolution infrared spectra obtained at In f raredTelescopeFacility. We confirm three of the candidates to be new members of the group: TYC 1186-706-1, TYC 7443-1102-1, and TYC 2211-1309-1 which are late-K and early-M dwarfs 45-60pc from the Sun. We also identify a common proper motion companion to the known β Pictoris Moving Group member TYC 7443-1102-1, at a 26 ′′ .3 separation; the new companion is associated with the X-ray source 1RXS J195602.8-320720. We argue that the present technique could be applied to other large proper motion catalogs to identify most of the elusive, low-mass members of known nearby moving groups and associations. Subject headings: astrometry -stars: emission-line, Be -stars: kinematics -stars: pre-main sequence -open clusters and associations: individual (β Pictoris Moving Group) 1 Based on data obtained in part with the 2.4 m Hiltner telescope of the MDM observatory.

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“…The prototypical example is perhaps the TW Hydrae association ( Kastner et al 1997), with an estimated age of 8-10 Myr and some two dozen members. Searches for new members of this group have relied on X-ray properties, kinematics, infrared ( Two Micron All Sky Survey [2MASS]) colors, and spectral features (e.g., Makarov & Fabricius 2001;Gizis 2002;Tachihara et al 2003;Song et al 2003) and have produced many candidates and motivated detailed follow-up studies to confirm them.…”

Section: Introductionmentioning

confidence: 99%

The Astrometric-Spectroscopic Binary System HIP 50796: An Overmassive Companion

Torres¹

2006

Astron J

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We report spectroscopic observations of the star HIP 50796, previously considered ( but later rejected) as a candidate member of the TW Hya association. Our measurements reveal it to be a single-lined binary with an orbital period of 570 days and an eccentricity of e ¼ 0:61. The astrometric signature of this orbit was previously detected by Hipparcos in the form of curvature in the proper-motion components, although the period was unknown at the time. By combining our radial velocity measurements with the Hipparcos intermediate data (abscissa residuals) we are able to derive the full three-dimensional orbit and determine the dynamical mass of the unseen companion, as well as a revised trigonometric parallax that accounts for the orbital motion. Given our primary mass estimate of 0.73 M (mid-K dwarf ), the companion mass is determined to be 0.89 M , or $20% larger than the primary. The likely explanation for the larger mass without any apparent contribution to the light is that the companion is itself a closer binary composed of M dwarfs. The near-infrared excess and X-ray emission displayed by HIP 50796 support this. Our photometric modeling of the excess leads to a lower limit to the mass ratio of the close binary of q $ 0:8 and individual masses of 0.44-0.48 and 0.41-0.44 M . The new parallax ( ¼ 20:6 AE 1:9 mas) is significantly smaller than the original Hipparcos value and more precise.

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Proper motion and X‐ray selected search for new members of the young TW Hya association

Cited by 5 publications

References 34 publications

BANYAN. IX. The Initial Mass Function and Planetary-mass Object Space Density of the TW HYA Association

BANYAN. IX. The Initial Mass Function and Planetary-mass Object Space Density of the TW HYA Association

Nearby Young Stars Selected by Proper Motion. I. Four New Members of the Β Pictoris Moving Group From the Tycho-2 Catalog

The Astrometric-Spectroscopic Binary System HIP 50796: An Overmassive Companion

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