A wide brown dwarf binary around a planet-host star

Transcription

1 A wide brown dwarf binary around a planet-host star Nicolas Lodieu (1, 2, 3) (1) Instituto de Astrofisica de Canarias (IAC, Tenerife) (2) Universidad de La Laguna (ULL, Tenerife) (3) Ramon y Cajal fellow at the IAC Collaborators: A. Pérez-Garrido, V. J. S. Béjar, R.Rebolo, & B. Gauza Brown dwarfs come of age, Fuerteventura Tuesday 21 May 2013

2 Goals and Outline 1) Scientific goals: 1) A complete census of the solar neighbourhood 2) Find benchmark L and T dwarfs 3) Uncover late-t and Y dwarfs 4) Role of binarity in formation of brown dwarfs and planets 2) Outline of the talk: Brown dwarfs vs Exoplanets VISTA: description and public surveys The VISTA Hemisphere Survey (VHS) New results from VHS 1) Isolated brown dwarfs in VHS 2) Low-mass stars and substellar benchmark companions 3) A wide brown dwarf binary to a planet-host star?

3 Brown dwarfs vs Exoplanets 888 extrasolar planets discovered 1281 L/T/Y dwarfs published Rv/ astrometry exoplanet.eu Transit μlensing Imaging Timing Total DwarfArchives.org SpT Numbers T eff L T Y First exoplanet discovered in 1995 (Mayor & Queloz) First brown dwarfs discovered in 1995 (Nakajima et al.; Rebolo et al.)

4 Part 1 VISTA

5 Description of VISTA VISTA = Visible and Infrared Survey Telescope for Astronomy 4-m class telescope equipped with the world largest NIR camera VIRCAM offers a FOV of 1.65 sq. deg. with a pixel scale of 0.34 VISTA started operations on 15 October 2009 ZYJHKs filters + 2 narrow-band filters 75% of VISTA dedicated to ESO public surveys

6 VISTA Public Surveys VHS Complementary VST public surveys ESO spectroscopic public surveys

7 The VISTA Hemisphere Survey Aim: Image the entire Southern sky i.e. ~20000 square degrees 1) 5000 sq. deg. in YJHKs around Galactic Caps 2) 5000 sq. deg. in JHKs linked to the Dark Energy Survey 3) sq. deg. in JKs (rest of the sky) Typical 5σ depths: J~19.5±0.3 mag and Ks~18.5±0.3 mag Science drivers: 1) Low-mass stars and nearby stars 2) Merger history of the Galaxy 3) High-redshift quasars 4) Measuring the properties of Dark Energy Principal Investigator: Richard McMahon, IoA, Cambridge (UK)

8 The VHS DR1 coverage

9 Part 2 New results from VHS

10 { Isolated cool brown dwarfs VHS vs WISE cross-match 1) Photometric selection criteria (w1-w2) 2.0 mag w2snr 3 VHS non detection No USNO counterpart Matching radius 5 2) NIR spectroscopic follow-up VLT/XSHOOTER: 0.3(0.8)-2.3 R~600 down to J~18.5 mag Magellan/FIRE: R~ down to J~19.5 mag ==> Spectroscopic confirmation of 7 late-t dwarfs identified in VHS/WISE Lodieu et al. (2012, A&A, 548, 53)

11 Benchmark companions to nearby stars Aim: Complete census of nearby high proper motion stars of any type Method: Cross-match VHS and 2MASS offering a baseline of >10 years Search limits: 1) Objects brighter than J = 16.5 mag 2) Proper motions larger than 0.2 arcsec/yr 3) Current overage: 1350 square degrees Results: New high proper motion stars and brown dwarfs 1) Discovery of LHS2803AB pair: dm + T6 at 67 arcsec (Muzic et al. (2012) 2) Discovery of a 4th component in the HD system, formed by a slightly metal-poor primary ([Fe/H]= 0.26) F8V and a distant M8V+L3V pair (Gauza et al. 2012) 3) Discovery of a wide T dwarf to a planet-host star

12 Part 3 A new wide companion to a planet host

13 Wide companions to planet-host stars (Mugrauer et al. 2007) Numbers of wide systems: 14 planet host star systems (Eggenberger 04) 2 additional system in 2005: HD (Eggenberger 05) and HD (Konacki 05) Discovery of ~15 companions with NTT/SofI with 2 epoch imaging (Mugrauer 04,05,07a,07b,09) New systems from WDS (Desidera & Barbieri 2007) 43 systems known as of 2009 (Mugrauer 09) Multiplicity rate of planet-host stars: 17-20% Properties of planets in wide binaries: Only systems with planets M > 3 MJup and P < 40 days (Zucker & Mazeh 2002; Eggenberger 04) No wide systems with e > 0.1 and P < 40 days Marginal difference for e > 0.6

14 1) The host star: Star and companion properties K7V star, Teff=4105±130K, age=3±2 Gyr, Mass=0.63 Msun (Segransan et al. 2011) d=23.57±1.22 pc (Hipparcos; van Leeuwen 2007), V=10.36 mag (Koen et al. 2010) Possible low metallicity: [Fe/H] = -0.2±0.1 Moderately active star 2) The planet: Planet detected by radial velocity in 2009 (Segransan et al. 2011) Msin(i) = 9±6 Mjup a= au, P= days, e= ) The wide companion: Identified in the WISE-VHS cross-match with 9 other potential candidates Located at ~6.5 arcmin (9360 au) from the planet-host star Jvhs = 15.54±0.01 mag, Ks = 15.50±0.02 mag, w2 = 13.85±0.05 mag Proper motion = (-0.038,-0.196) vs (-0.047,-0.204) mas/yr

15 A wide companion to HIP70849 HIP70849 T45 T45 HIP70849 All 2MASS/VHS sources with J<17 mag within 14 arcmin of the primary 1 sigma errors of 15.4 and 14.6 mas/yr Colour vs Absolute magnitude diagram L and T dwarfs with parallaxes (Vrba 2004) L/T sequence (Vrba+2004; Kirkpatrick+2011)

16 NTT/SofI spectroscopy Near-infrared spectroscopy: Observations on 29 December 2012 under photometric conditions ZJ+HK spectroscopy with NTT/SofI using slit of 1 arcsec Low-resolution R~600, covering & µm ExpT=16 min and 40 min for ZJ and HK gratings, respectively Spectral standard of A0-type for telluric correction Standard data reduction with IRAF

17 Near-infrared spectrum SpT = T4.5 Teff ~ 1240±50 d = pc T4+T5 is possible First wide brown dwarf binary to a planet-host star?

18 Conclusions 1) Exploitation of the VHS coverage: Discovery of the first T dwarfs in VHS Discovery of a quadruple system (Lodieu et al. 2012, A&A, 548, 53) (Gauza et al. 2012, MNRAS, 427, 2457) Discovery of new wide companions to planet-host stars Discovery of the first BD binary around a host star? Discovery of new high proper motion L and T dwarfs (Lodieu et al. 2013, in prep) 2) Future work: On-going GTC/OSIRIS optical spectroscopic follow-up On-going NTT SofI+EFOSC2 optical+infrared spectroscopic follow-up Determine the frequency of wide companions to planet-host stars Determine the frequency of L and T dwarfs around nearby stars