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Crossing into the substellar regime in Praesepe

journal contribution
posted on 2023-05-17, 14:36 authored by Chappelle, RJ, Pinfield, DJ, Steele, IA, Dobbie, PD, Magazzu, A
We present the results of a deep optical 2.6 deg2 survey with near-infrared (NIR) follow-up measurements of the intermediate-aged Praesepe open cluster. The survey is complete to Ic = 21.3, Z = 20.5, corresponding to M ∼ 0.06 M⊙ assuming a cluster age of 0.5 Gyr. Using three to five passbands to constrain cluster membership, we identify 32 new low-mass cluster members, at least four of which are likely to be substellar. We use the low-mass census to trace the region where the sequence moves away from the NEXTGEN towards the DUSTY regime at Teff = 2200 K. In doing so, we identify four unresolved binaries, yielding a substellar binary fraction (BF) of ∼30 per cent. The BFs appear to decrease below 0.1 M⊙, in contrast to the rising fractions found in the Pleiades. We also identify a paucity of late M dwarfs, thought to be due to a steepening in the mass–luminosity relation at these spectral types, and compare the properties of this gap in the sequence to those observed in younger clusters. We note an overdensity of faint sources in the region of the so-called subcluster (possibly an older smaller cluster within Praesepe), and subsequently derive the luminosity and mass functions (MFs) for the main Praesepe cluster, revealing a turnover near the substellar boundary. We conclude by presenting astrometric measurements for low-mass Praesepe candidates from the literature and rule out as a likely foreground dwarf RPr1, hitherto thought to be a substellar member.

History

Publication title

Monthly Notices of the Royal Astronomical Society

Volume

361

Issue

4

Pagination

1323-1336

ISSN

0035-8711

Department/School

School of Natural Sciences

Publisher

Blackwell Publishing Ltd

Place of publication

9600 Garsington Rd, Oxford, England, Oxon, Ox4 2Dg

Rights statement

Copyright 2005 RAS

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the physical sciences

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