Protostars and Planets V 2005 8327.pdf

DIRECT IMAGING OF EXTRA-SOLAR PLANETS – THE CASE OF GQ LUPI A AND B. R. Neuhäuser1, M. Mugrauer1, G. Wuchterl1, E.W. Guenther2, A. Bedalov1, P. Hauschildt3, 1Astrophysikalisches Institut und Universitäts-Sternwarte, Universität Jena, Schillergäßchen 2-3, D-07745 Jena, Germany, [email protected], 2Thüringer Landessternwarte, D-07778 Tautenburg, Germany, 3Hamburger Sternwarte, D-21029 Hamburg, Germany

Introduction: We have presented direct evidence This is consistent with the color K-L = 1.4 +/- 0.3 mag for a sub-stellar companion around the classical T found for the companion and indicates that its assumed Tauri GQ Lup in the I cloud, which could extinction is the same as known for the primary [1]. be of planetary . In this poster, we summarize and The primary star has K7eV spectral type. The discuss our evidence, presented in detail in [1] and [2]. magnitude difference of 6 mag in K at the young age We also compare the GQ Lup A+b pair with the (1-2 Myrs) is consistent with the spectral type early-L 2M1207 pair, which may neither be bound nor stable. found for the companion, which is another indidation Direct imaging detection: We detected the for it being a bound companion. companion of GQ Lup with the AO instrument NaCo Mass estimation: From the spectrum, we could at the VLT in June 2004. The companion candidate is not only determine temperature (T~2000 K) and flux, 6 mag fainter than the primary, detected in K and L, but also the gravity of the companion, being log g = 2 and 0.7 arc sec west of the primary, i.e. ~100 AU at to 3, from fits to GAIA-dusty template spectra [3] This ~140 pc [1]. The companion candidate was also estimate is consistent with a gravity estimate from only detected by Subaru/CIAO in 2002 and HST/PC in the CO lines. Hence, from the flux, temperature, and 1999, so that we could investigate its . distance, we could determine the radius to be 1.2 +/- Common proper motion: There are six proper 0.5 Jup radii, and then from radius and gravity the motions published for the GQ Lup primary, which mass of the companion, namely below 1 Jup mass; argree with eachother within 2 sigma error bars. We with log g = 4 and 2 Jup radii still below 6 Jup determined the weighted mean proper motion to be - [1]. 19.15 +/- 1.67 mas/yr in RA and -21.06 +/- 1.69 Because of the young age of GQ Lup A and its mas/yr in Dec [2]. Using this proper motion and companion (below 2 Myrs), conventional evolutionary comparing the three measurements for separation and models such as from the Lyon or Tucson groups position angle between the primary GQ Lup A and the cannot be applied and used here. They start with companion, we obtain the signifiance for common assumed initial conditions and do not take into account proper motion to be 7+4+8 sigma [2]. This is even the collapse and accretion phase. Hence, they cannot higher than given in [1], where we have used one be used to determine the mass of the companion. (If particular proper motion value. For any proper motion one would do so, the mass estimate would be published for GQ Lup A, there is high significance for anywhere between 3 and 42 Jup masses, so that it common proper motion [1,2]. The large error in the would be a planet or brown dwarfs [1].) distance towards GQ Lup (140 +/- 50 pc) affects the The model by [4] does take into account the significance in common proper motion by only 0.2 dex collapse, so that it can be applied. Having calculated [2]. Hence, the companion candidate cleary shares the the luminosity (from the K-band mag, the B.C. for M9- proper motion of its primary. L4, and the distance) and the temperature (being 2050 Most objects in the Lupus T association share the +/- 450 K, from the spectral type and considering all same proper motion, as it is a moving group. Hence, it published conversions), we can place the object into could in principle be possible that GQ Lup A and the the H-R diagram as shown in [1]. The mass of the faint object with almost the same proper motion both companion is then 1 to 3 Jup masses being co-eval are independant members of the Lupus association, but with the primary at ~1 Myr. The model given in [4] do not orbit eachother. However, this is a very unlikely and used in [1] has in the meantime been shown to case: The probability to find a faint early L-dwarf at reproduce the masses, ages, radii, tempratures, and almost the same position with almost the same proper gravities of the low-mass objects studied in [5,6] very motion as GQ Lup A is less than 3e-10 [2]. well. Spectroscopy: Our K-band spectrum of the Hence, according to both estimations, the companion, also taken with NaCo at the VLT, shows a companion has a mass below 13 Jup masses, so that is depression in the blue wing, typical for water can be considered a planet, called GQ Lup b. absorption in L-dwarfs, and also CO and possibly GQ Lup b also has lower luminosity, younger age, weak Na. The continuum shape and spectral indices cooler spectral type, and fainter magnitude than the indicate M9 to L4 (probably L1-2) as spectral type. lowest-mass (free-floating) object studied in detail by

Protostars and Planets V 2005 8327.pdf

high-resolution spectroscopy in [5], which has only 9 whether the system is bound, see [2]. Jup masses [6] or maybe up to 15 Jup masses [7]. The question, whether a common proper motion Therefore, GQ Lup b must be lower in mass, hence pair is long-term stable against encounters with other most certainly a planet. and clouds in the , depends on the Formation of GQ Lup b as planet: If GQ Lup b component masses and the separation. According to is indeed a planet, the first imaged directly, being the criteria given in [9] and the bounding energy of the located 100 AU west of its primary star, the question GQ Lup and 2M1207 systems, the GQ Lup A+b arises as to how it may have formed: system is long-term stable (similar to the giant planets (i)Circumstellar disks are often 100 AU or larger in in our solar system), while the 2M1207 system is not size, so that a planet may have formed in a long-term stable, and either has already separated or massive large disk; GQ Lup A has strong IR will disrupt soon. There is no wide, very-low mass excess, hence circumstellar material, possibly in binary known with such a low binding energy as form of a disk. 2M1207. See [2] for a discussion. The 2M1207 system (ii)Planets and planet candidates found by the can be bound and long-term stable, only if the total radial velocity technique, often have eccentric mass is much larger than given in [8]. If 2M1207 is orbits; GQ Lup b may be in a strongly eccentric closer than 50 to 70 pc and possibly also a bit hotter orbit with semi-major axis much smaller than than given in [8], then it falls onto or near the H- or D- 100 AU. burning (main) sequence of calculations in [4], so that (iii) GQ Lup b and another protoplanet may have the masses of both its components are larger. encountered a near-encounter, which led to an The temperature of is given to be only outward migration of GQ Lup b (which may 1000 to 1600 K [8], obtained from its observed still be bound, though); the other protoplanet magnitudes and conventional (Lyon and Tucson) may have migrated inwards, possibly to be models. Those models are, however, probably not discovered later. applicable for the 2M1207 system, if indeed a member Comparing GQ Lup with 2M1207: The possible of the 5-12 Myr young TWA. Also, the conventional remaining motion between GQ Lup A and b is 1.4 +/- models are known to give temperatures which are too 2.2 mas/yr, by comparing the three epochs. The orbital cool. motion to be expected is roughly 3.7 +/- 1.5 mas/yr, If one would convert its observed spectral type L5- consistent with the possible motion observed, but not 9 [8] to a tempearture by using published conversions, yet detected. The escape velocity of GQ Lup b would as it is normally done, then one arrives at 1100 to 2000 be 5.2 +/- 2.1 mas/yr, i.e. larger than the observed K, i.e. probably hotter then given in [8]. If it is hotter, possible motion, so that the system is bound. than it is also higher in mass and, hence, could then be This is not yet shown for the 2M1207 system, (long-term) stable. where an L5-9 dwarf shares the same proper motion References: [1] Neuhäuser R. et al. (2005) A&A, with a proposed M9 member of the TW Hya 435, L13. [2] Mugrauer M. and Neuhäuser R. (2005) association, with mass estimates as low as 5 and 25 Jup AN, submitted. [3] Brott and Hauschildt, in prep. masses [8]. Here, the remainng possible motion [4] Wuchterl G. and Tscharnuter W. (2003) A&A 398, between A and b is 4.1 +/- 8.2 mas/yr (see [8]), to be 1081. [5] Mohanty S. et al. (2004) ApJ 609, 854. [6] compared to the expected orbital motion of 1.9 +/- 0.6 Mohanty S. et al. (2004) ApJ 609, 885. [7] Reiners A., mas/yr and the escape velocity of 2.7 +/- 0.9 mas/yr. private communication. [8] Chauvin G. et al. (2005) Because the possible motion is not yet shown to be A&A 438, L25. [9] Close L. et al. (2003) ApJ 587, smaller than the escape velocity, it is not yet clear 407.