The DODO Survey II: A Gemini Direct Imaging Search for Substellar and Planetary Mass Companions around Nearby Equatorial and Northern Hemisphere W

📝 Abstract

The aim of the Degenerate Objects around Degenerate Objects (DODO) survey is to search for very low mass brown dwarfs and extrasolar planets in wide orbits around white dwarfs via direct imaging. The direct detection of such companions would allow the spectroscopic investigation of objects with temperatures much lower (< 500 K) than the coolest brown dwarfs currently observed. These ultra-low mass substellar objects would have spectral types > T8.5 and so could belong to the proposed Y dwarf spectral sequence. The detection of a planet around a white dwarf would prove that such objects can survive the final stages of stellar evolution and place constraints on the frequency of planetary systems around their progenitors (with masses between 1.5 - 8 solar masses, i.e., early B to mid F). This paper presents the results of a multi-epoch J band common proper motion survey of 23 nearby equatorial and northern hemisphere white dwarfs. We rule out the presence of any common proper motion companions, with limiting masses determined from the completeness limit of each observation, to 18 white dwarfs. For the remaining five targets, the motion of the white dwarf is not sufficiently separated from the non-moving background objects in each field. These targets require additional observations to conclusively rule out the presence of any common proper motion companions. From our completeness limits, we tentatively suggest that < 5% of white dwarfs have substellar companions with effective temperatures > 500 K between projected physical separations of 60 - 200 AU.

💡 Analysis

The aim of the Degenerate Objects around Degenerate Objects (DODO) survey is to search for very low mass brown dwarfs and extrasolar planets in wide orbits around white dwarfs via direct imaging. The direct detection of such companions would allow the spectroscopic investigation of objects with temperatures much lower (< 500 K) than the coolest brown dwarfs currently observed. These ultra-low mass substellar objects would have spectral types > T8.5 and so could belong to the proposed Y dwarf spectral sequence. The detection of a planet around a white dwarf would prove that such objects can survive the final stages of stellar evolution and place constraints on the frequency of planetary systems around their progenitors (with masses between 1.5 - 8 solar masses, i.e., early B to mid F). This paper presents the results of a multi-epoch J band common proper motion survey of 23 nearby equatorial and northern hemisphere white dwarfs. We rule out the presence of any common proper motion companions, with limiting masses determined from the completeness limit of each observation, to 18 white dwarfs. For the remaining five targets, the motion of the white dwarf is not sufficiently separated from the non-moving background objects in each field. These targets require additional observations to conclusively rule out the presence of any common proper motion companions. From our completeness limits, we tentatively suggest that < 5% of white dwarfs have substellar companions with effective temperatures > 500 K between projected physical separations of 60 - 200 AU.

📄 Content

arXiv:0901.0532v1 [astro-ph.EP] 5 Jan 2009 Mon. Not. R. Astron. Soc. 000, 000–000 (0000) Printed 26 October 2021 (MN LATEX style file v2.2) The DODO Survey II: A Gemini Direct Imaging Search for Substellar and Planetary Mass Companions around Nearby Equatorial and Northern Hemisphere White Dwarfs E. Hogan,1,2 M.R. Burleigh,1 and F.J. Clarke3 1Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK 2Gemini Observatory, Casilla 603, La Serena, Chile 3Department of Astrophysics, Denys Wilkinson Building, University of Oxford, Keble Road, Oxford, OX1 3RH, UK 26 October 2021 ABSTRACT The aim of the Degenerate Objects around Degenerate Objects (DODO) survey is to search for very low mass brown dwarfs and extrasolar planets in wide orbits around white dwarfs via direct imaging. The direct detection of such companions would allow the spectroscopic investigation of objects with temperatures much lower (< 500 K) than the coolest brown dwarfs currently observed. These ultra–low mass substellar objects would have spectral types >T8.5 and so could belong to the proposed Y dwarf spectral sequence. The detection of a planet around a white dwarf would prove that such objects can survive the final stages of stellar evolution and place constraints on the frequency of planetary systems around their progenitors (with masses between 1.5 −8 M⊙, i.e., early B to mid F). This paper presents the results of a multi–epoch J band common proper motion survey of 23 nearby equatorial and northern hemisphere white dwarfs. We rule out the presence of any common proper motion companions, with limiting masses determined from the completeness limit of each observation, to 18 white dwarfs. For the remaining five targets, the motion of the white dwarf is not sufficiently separated from the non–moving background objects in each field. These targets require additional observations to conclusively rule out the presence of any common proper motion companions. From our completeness limits, we tentatively suggest that ≲5% of white dwarfs have substellar companions with Teff≳500 K between projected physical separations of 60 −200 AU. Key words: stars: white dwarfs; planetary systems; low mass, brown dwarfs; imaging. 1 INTRODUCTION Directly imaging the extrasolar planets found in orbit around solar type stars is difficult as these faint compan- ions are too close to their bright parent stars. As this paper was being finalised, Kalas et al. (2008) announced the dis- covery of a directly imaged ∼3 MJup extrasolar planet with a projected physical separation of 119 AU in orbit around the A-type star Fomalhaut. On the same day, Marois et al. (2008) announced the discovery of three directly imaged companions around the A-type star HR8799 with likely masses between 5 −13 MJup and projected physical sepa- rations of 24, 38 and 68 AU. However, coronagraphy and adaptive optics were needed to detect these faint extraso- lar planets. Another, perhaps simpler, solution to the prob- lems of contrast and resolution is to instead target intrin- sically faint stars. For example, many groups are already searching for planetary mass companions1 in orbit around young, low mass stars and brown dwarfs (e.g., Chauvin et al. 2003; Neuh¨auser et al. 2003). Any planetary mass compan- ions found in orbit around these young stars will have 1 We make the distinction between very low mass brown dwarfs and massive extrasolar planets by formation mechanism rather than mass, since the mass distributions of these two types of object likely overlap. For example, the 9 MJup transiting object HAT-P-2b is too dense to be a brown dwarf (Baraffe et al. 2008), while the free floating objects with masses of the order of a few Jupiter masses that have been found in young clusters possibly formed in the same manner as stars. Indeed, some authors insist that the IAU distinction between these two populations, based on mass alone, has no valid foundation (Chabrier et al. 2008). There- fore, throughout this paper we prefer to use the term ”planetary mass object” to refer to any body at or below the deuterium burning limit (13 −14 MJup), since the evolutionary history of any companions discovered with these masses is uncertain. 2 E. Hogan et al. relatively high luminosities, since planetary mass objects cool continuously from the moment they form. Famously, a ∼4 ± 1 MJup (Ducourant et al. 2008) companion to the ∼25 MJup brown dwarf member of the TW Hydrae associa- tion 2MASSW J1207334 −393254 (2M1207) was imaged by Chauvin et al. (2004, 2005). However, Lodato et al. (2005) argue that 2M1207Ab more likely formed as a binary brown dwarf system, since the core accretion model, thought to be the most likely formation mechanism for gas giants like those in the Solar System, is unable to account for the formation of 2M1207b. An alternative approach, rather than looking at the bright, early part of a planet’s life, is to look at the faint, late part of a star’s life. Whit

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