SPHERE dynamical and spectroscopic characterization of HD 142527B^⋆,⋆⋆

¹ INAF – Osservatorio Astronomico di Padova, Italy
e-mail: riccardo.claudi@oapd.inaf.it
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ INCT, Universidad De Atacama, calle Copayapu 485, Copiapó, Atacama, Chile
⁴ Geneva Observatory, University of Geneva, Chemin des Maillettes 51, 1290 Versoix, Switzerland
⁵ SUPA, Institute for Astronomy, The University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁶ Núcleo de Astronomia, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejercito, Santiago, Chile
⁷ Escuela de Ingeniería Industrial, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
⁸ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁹ ETH Zurich, Institute for Astronomy, Wolfgang-Pauli-Str. 27, 8093 Zurich, Switzerland
¹⁰ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹¹ Millennium Nucleus “Protoplanetary Disk”, Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹² LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
¹³ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹⁴ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹⁵ Unidad Mixta Internacional Franco–Chilena de Astronomia, CNRS/INSU UMI 3386 and Departemento de Astronomía, Universidad de Chile, Casilla 36–D, Santiago, Chile
¹⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁷ Department of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
¹⁸ Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA
¹⁹ CRAL, UMR 5574, CNRS, Université de Lyon, École Normale Supérieure de Lyon, 46 allée d’Italie, 69364 Lyon Cedex 07, France
²⁰ INAF–Catania Astrophysical Observatory, via S. Sofia, 78, 95123 Catania, Italy
²¹ York Creek Observatory, Georgetown 7253, TAS, Australia
²² Department of Astronomy, University of Michigan, 1085 S. University, Ann Arbor, MI 48109, USA
²³ Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
²⁴ Núcleo Milenio Formación Planetaria – NPF, Universidad de Valparaíso, Av. Gran Bretaña 1111, Valparaíso, Chile
²⁵ Monash Centre for Astrophysics (MoCA) and School of Physivs and Astronomy Monash University, Clayton, Vic, 3800 Australia
²⁶ Xi’an Jiaotong–Liverpool University, department of Mathematical Sciences, 111 Ren’ai road, Suzhou Dushu Lake Higher Education town, Jiangsu Province 215123, PR China
²⁷ NOVA Optical Infrared Instrumentation Group, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands

Received: 30 July 2018
Accepted: 3 December 2018

Abstract

Aims. HD 142527 is one of the most frequently studied Herbig Ae/Be stars with a transitional disk that hosts a large cavity that is up to about 100 au in radius. For this reason, it has been included in the guaranteed time observation (GTO) SpHere INfrared survey for Exoplanets (SHINE) as part of the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) at the Very Large Telescope (VLT) in order to search for low-mass companions that might explain the presence of the gap. SHINE is a large survey within about 600 young nearby stars are observed with SPHERE with the aim to constrain the occurrence and orbital properties of the giant planet population at large (> 5 au) orbital separation around young stars.

Methods. We used the IRDIFS observing mode of SPHERE (IRDIS short for infrared dual imaging and spectrograph plus IFS or integral field spectrograph) without any coronagraph in order to search for and characterize companions as close as 30 mas of the star. Furthermore, we present the first observations that ever used the sparse aperture mask (SAM) for SPHERE both in IRDIFS and IRDIFS_EXT modes. All the data were reduced using the dedicated SPHERE pipeline and dedicated algorithms that make use of the principal component analysis (PCA) and reference differential imaging (RDI) techniques.

Results. We detect the accreting low–mass companion HD 142527B at a separation of 73 mas (11.4 au) from the star. No other companions with mass greater than 10 M_J are visible in the field of view of IFS (∼100 au centered on the star) or in the IRDIS field of view (∼400 au centered on the star). Measurements from IFS, SAM IFS, and IRDIS suggest an M6 spectral type for HD 142527B, with an uncertainty of one spectral subtype, compatible with an object of M = 0.11 ± 0.06 M_⊙ and R = 0.15 ± 0.07 R_⊙. The determination of the mass remains a challenge using contemporary evolutionary models, as they do not account for the energy input due to accretion from infalling material. We consider that the spectral type of the secondary may also be earlier than the type we derived from IFS spectra. From dynamical considerations, we further constrain the mass to 0.26^+0.16_−0.14 M_⊙, which is consistent with both our spectroscopic analysis and the values reported in the literature. Following previous methods, the lower and upper dynamical mass values correspond to a spectral type between M2.5 and M5.5 for the companion. By fitting the astrometric points, we find the following orbital parameters: a period of P = 35 − 137 yr; an inclination of i = 121 − 130°, a value of Ω = 124 − 135° for the longitude of node, and an 68% confidence interval of ∼18 − 57 au for the separation at periapsis. Eccentricity and time at periapsis passage exhibit two groups of values: ∼0.2–0.45 and ∼0.45–0.7 for e, and ∼2015–2020 and ∼2020–2022 for T₀. While these orbital parameters might at first suggest that HD 142527B is not the companion responsible for the outer disk truncation, a previous hydrodynamical analysis of this system showed that they are compatible with a companion that is able to produce the large cavity and other observed features.