DISCOVERY OF Hα EMISSION FROM THE CLOSE COMPANION INSIDE THE GAP OF TRANSITIONAL DISK HD 142527

Abstract

We utilized the new high-order 585 actuator Magellan Adaptive Optics system (MagAO) to obtain very high-resolution visible light images of HD142527 with MagAO's VisAO science camera. In the median seeing conditions of the 6.5m Magellan telescope (0.5 − 0.7′′), we find MagAO delivers 24-19% Strehl at Hα (0.656 µm). We detect a faint companion (HD142527B) embedded in this young transitional disk system at just 86.3±1.9 mas (~12 AU) from the star. The companion is detected in both Hα and a continuum filter (∆mag=6.33±0.20 mag at Hα and 7.50±0.25 mag in the continuum filter). This provides confirmation of the tentative companion discovered by Biller and co-workers with sparse aperture masking at the 8m VLT. The Hα emission from the ~0.25 solar mass companion (EW=180 Angstroms) implies a mass accretion rate of ~5.9x10 -10 M sun /yr, and a total accretion luminosity of 1.2% L sun . Assuming a similar accretion rate, we estimate that a 1 Jupiter mass gas giant could have considerably better (50-1000x) planet/star contrasts at Hα than at H band (COND models) for a range of optical extinctions (3.4-0 mag). We suggest that ~0.5-5 M jup extrasolar planets in their gas accretion phase could be much more luminous at Hα than in the NIR. This is the motivation for our new MagAO GAPplanetS survey for extrasolar planets.

Characterization of exoplanets from their formation

“…Recently, several discoveries of (candidate) low-mass companions (low-mass stars and protoplanets) embedded in the circumstellar disk of young stars were announced: around LkCa 15 (Kraus & Ireland 2012), HD 142527 (Biller et al 2012), HD 100546 (Quanz et al 2013), and HD 169142 (Reggiani et al 2014;Biller et al 2014). While the exact nature of some of these sources needs to be further investigated, some of these objects are probably indeed observed in the act of formation as indicated by the Hα emission of LkCa 15 b Sallum et al (2015) (see also HD 142527B, Close et al 2014). This warrants an extension of the M − L relation to the formation phase.…”

“…If the planetary and stellar accretion rates are of the same order of magnitude as suggested by hydrodynamic simulations (Lubow & D'Angelo 2006), then the independency of R on M for cold accretion can be used to estimate, via L est , the planet's mass pro- vided that L shock can be observationally obtained. This approach (see also Kraus & Ireland 2012;Close et al 2014) then yields a constraint on the planet's mass besides other indicators such as the gap morphology (e.g., Kanagawa et al 2015) or the local disk temperature (Montesinos et al 2015) and scale height (Klahr & Kley 2006). For hot accretion it is more complex to estimate the planet's mass in this way, as the radius becomes then also a function of mass (Fig.…”

“…The comparison with LkCa 15b is found in the next section. The L Hα of HD 142527 B (Close et al 2014), which is a low-mass M dwarf (Lacour et al 2016), is also shown for comparison.…”

“…In only the last few years, cutting-edge observations have caught a small number of putative low-mass companions in their mass-assembly phase (around LkCa 15, HD 142527, HD 100546, and HD 169142;Kraus & Ireland 2012;Sallum et al 2015;Close et al 2014;Quanz et al 2013;Reggiani et al 2014). These fascinating observations of planet formation as it happens provide an additional motivation to study the luminosity of planets already during the formation phase, whether or not their radiation can leave relatively unimpeded their natal circumstellar and -planetary disk(s).…”

Detection limits with spectral differential imaging data

“…SDI was first used on the Canada France Hawaii Telescope (CFHT) with the TRIDENT camera (Marois et al 2000(Marois et al , 2003a, with NaCo on the Very Large Telescope (VLT/NaCo; Lenzen et al 2003;Rousset et al 2003) and with the Multiple Mirror Telescope (MMT) A&A 581, A80 (2015) by Close et al (2005) and Biller et al (2007). Recently, Close et al (2014) confirmed a close-in companion around HD 142527 with SDI with MagAO, based on a detection of the Hα emission, not a molecular absorption. However, SDI is limited by differential aberrations between the two channels, which create quasi-static speckles that cannot be removed.…”