2010A&A...516A.112N


Query : 2010A&A...516A.112N

2010A&A...516A.112N - Astronomy and Astrophysics, volume 516, A112-112 (2010/6-3)

Orbital motion of the young brown dwarf companion TWA 5 b.

NEUHAEUSER R., SCHMIDT T.O.B., HAMBARYAN V.V. and VOGT N.

Abstract (from CDS):

It is difficult to determine masses and test formation models for brown dwarfs, because they are always above the main sequence, so that there is a degeneracy between mass and age. However, for brown dwarf companions to normal stars, such determinations may be possible, because one can know the distance and age of the primary star. As a result, brown dwarf companions are well-suited to testing formation theories and atmosphere models. With more adaptive optics images available, we aim at detecting orbital motion for the first time in the system TWA 5 A+B. We measured separation and position angle between TWA 5 A and B in each high-resolution image available and followed their change in time, because B should orbit around A. The astrometric measurement precision is about one milli arcsec. With ten year difference in epoch, we can clearly detect orbital motion of B around A, a decrease in separation by ∼0.0054'' per year and a decrease in position angle by ∼0.26° per year. TWA 5 B is a brown dwarf with ∼25 Jupiter masses (Neuhaeuser et al., 2000A&A...360L..39N), but having large error bars (4 to 145 Jupiter masses, Neuhaeuser et al., 2009, AIPC, 1094, 884). Given its large projected separation from the primary star, ∼86AU, and its young age (∼10Myr), it has probably formed star-like, and would then be a brown dwarf companion. Given the relatively large changes in separation and position angle between TWA 5 A and B, we can conclude that they orbit around each other on an eccentric orbit. Some evidence is found for a curvature in the orbital motion of B around A - most consistent with an elliptic (e=0.45) orbit. Residuals around the best-fit ellipse are detected and show a small-amplitude (∼18mas) periodic sinusoid with ∼5.7yr period, i.e., fully consistent with the orbit of the inner close pair TWA 5 Aa+b. Measuring these residuals caused by the photocenter wobble - even in unresolved images - can yield the total mass of the inner pair, so can test theoretical pre-main sequence models.

Abstract Copyright:

Journal keyword(s): astrometry - binaries: visual - brown dwarfs - stars: formation - stars: individual: TWA 5 - stars: pre-main sequence

Simbad objects: 12

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Number of rows : 12
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
#notes
1 TWA 22 LXB 10 17 26.8927745040 -53 54 26.387425044   15.69 13.96 13.72   M5 77 0
2 V* TW Hya TT* 11 01 51.9053285064 -34 42 17.033218380   11.94 10.50 10.626 9.18 K6Ve 1791 1
3 NAME TW Hya Association As* 11 01.9 -34 42           ~ 907 0
4 HD 98800 TT* 11 22 05.28975 -24 46 39.7571   10.20 9.28 9.26 7.386 K5V(e) 359 0
5 CD-33 7795B LM* 11 31 55.2500 -34 36 25.200     20.40   15.8 M8.5/9e 120 0
6 CD-33 7795 TT* 11 31 55.2608963280 -34 36 27.203892120   12.97 11.524 11.150 9.150 M2Ve 187 0
7 HD 102458 Y*O 11 47 24.5438206248 -49 53 03.018484572   9.70 9.07   8.40 G4V 88 0
8 CD-36 7429A TT* 11 48 24.2227406904 -37 28 49.114270524   12.54 11.17 10.92 9.552 K5V 120 0
9 CD-36 7429 ** 11 48 24.22320 -37 28 49.1537           ~ 95 0
10 TWA 27 LM* 12 07 33.4675524840 -39 32 54.016625184     19.95 17.99 15.88 M8IVe 330 0
11 HD 109573 PM* 12 36 01.0317461592 -39 52 10.220465388   5.786 5.774 7.25 5.81 A0V 603 1
12 HD 132347 ** 14 59 29.23211 -30 42 41.5076           A3mA5-F0 23 0

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2023.02.03-23:49:58

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