Candidate free-floating super-Jupiters in the young <i>σ</i> Orionis open cluster

Bihain, G.; Rebolo, R.; Osorio, M. R. Zapatero; Béjar, V. J. S.; Villó-Pérez, Isidro; Díaz‐Sánchez, A.; Pérez‐Garrido, A.; Caballero, J. A.; Bailer‐Jones, C. A. L.; Barrado, D.; Eislöffel, J.; Forveille, T.; Goldman, B.; Henning, Th.; Martín, E. L.; Mundt, R.

doi:10.1051/0004-6361/200912210

Cited by 65 publications

(95 citation statements)

References 65 publications

(67 reference statements)

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“…In others, like the σ Orionis open cluster (Bihain et al 2009;Caballero et al 2007;Lodieu et al 2009;Peña Ramírez et al 2012) and in the Pleiades (Bihain et al 2006;Zapatero Osorio et al 2014) a decline is not obvious near the HBML. All mass distributions appear to show a continuous transition from BDs to stars, albeit exhibiting different gradients.…”

Section: Continuity Of the Imf At The Vlms -Bd Transitionmentioning

confidence: 96%

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

Marks¹,

Martín

Béjar

et al. 2017

A&A

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Context. Whether brown dwarfs (BDs) form just as stars directly from the gravitational collapse of a molecular cloud core ("star-like") or whether BDs and some very low-mass stars (VLMSs) constitute a separate population which form alongside stars comparable to the population of planets, e.g. through circumstellar disk ("peripheral") fragmentation, is one of the key questions of the star-formation problem. Aims. For young stars in Taurus-Auriga the binary fraction has been shown to be large with little dependence on primary mass above ≈ 0.2M⊙, while for BDs it is < 10%. Here we investigate a case in which BDs in Taurus formed dominantly, but not exclusively, through peripheral fragmentation, which naturally results in low binary fractions. The decline of the binary frequency in the transition region between star-like formation and peripheral formation is modelled. Methods. A dynamical population synthesis model is employed in which stellar binary formation is universal with a large binary fraction close to unity. Peripheral objects form separately in circumstellar disks with a distinctive initial mass function (IMF), own orbital parameter distributions for binaries and a low binary fraction according to observations and expectations from smoothed particle hydrodynamics (SPH) and grid-based computations. A small amount of dynamical processing of the stellar component is accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. Results. The binary fraction declines strongly in the transition region between star-like and peripheral formation, exhibiting characteristic features. The location of these features and the steepness of this trend depend on the masslimits for star-like and peripheral formation. Such a trend might be unique to low density regions like Taurus which host dynamically largely unprocessed binary populations in which the binary fraction is large for stars down to M-dwarfs and low for BDs. Conclusions. The existence of a strong decline in the binary fraction -primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star forming region. It is a test of the (non-)continuity of star formation along the mass-scale, the separateness of the stellar and BD populations and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.

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Section: Continuity Of the Imf At The Vlms -Bd Transitionmentioning

confidence: 96%

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

Marks¹,

Martín

Béjar

et al. 2017

A&A

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“…1, I noted the importance of a correct de-contamination before deriving any typical parameter in studies of star-forming regions. For example, special care has been applied when measuring the shape of the initial mass function in σ Orionis (see extensive de-contamination discussion in, e.g., Caballero et al 2007;Lodieu et al 2009;and Bihain et al 2009). However, I warn against the incorrect use of certain parameters that were derived without a correct de-contamination:…”

Section: Caveatsmentioning

confidence: 99%

“…Although it is not as young and nearby as other star-forming regions such as the Orion Nebula Cluster, ρ Ophiuchi, or Chamaeleon I+II, σ Orionis has the great advantage of being relatively compact (ρ core ∼ 20 arcmin -Caballero 2008a) and having a very low visual extinction (0.04 mag < E(B − V) < 0.09 mag - Béjar et al 2004;Sherry et al 2008). The high spatial density and low extinction do not only facilitate the study of the initial mass function down to well below the deuterium burning limit (Zapatero Osorio et al 2000;Béjar et al 2001;Caballero et al 2007;Bihain et al 2009), but also the identification and characterisation of young stars with X-ray emission (Sanz-Forcada et al 2004;Franciosini et al 2006;Skinner et al 2008;Caballero et al 2009) or discs detected on the basis of their infrared excess Hernández et al 2007;Zapatero Osorio et al 2007;Luhman et al 2008), hydrogen recombination lines in emission (including Hα -Zapatero Osorio et al 2002;Weaver & Babcock 2004;Kenyon et al 2005;Gatti et al 2008;Fedele et al 2010), or jets (Reipurth et al 1998;Andrews et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Stars and brown dwarfs in theσ Orionis cluster

Caballero¹

2010

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Aims. I attempt to fully understand the origin of the stellar and substellar populations in the young σ Orionis open cluster, which is a benchmark for star-forming studies. Because of the very low proper motion of the cluster, late-type dwarfs with appreciable proper motion in the foreground of σ Orionis can be easily discarded as targets from expensive spectroscopic follow-up studies. Methods. I use the Aladin sky atlas, USNO-B1, public astrometric catalogues, and photographic plate digitisations to identify stars with proper motions that are inconsistent with cluster membership in a circular area of radius 30 arcmin centred on the early-type multiple system σ Ori. Primarily because of the long time baseline of more than half a century, the errors in the measured proper motions are lower than 2 mas a −1 . Results. Of the 42 stars selected for astrometric follow-up, 37 of them are proper-motion cluster interlopers. Some USNO-B1 measurements were affected by partially resolved (visual) multiplicity and target faintness. Because of their late spectral types and, hence, red colours, 24 contaminants had been considered at some point as σ Orionis members. I discuss how contamination may have affected previous work (especially related to disc frequencies) and the curious presence of lithium absorption in three M-dwarf proper motion contaminants. Finally, I classify the bright star HD 294297 as a late-F field dwarf unrelated to the cluster based on a new proper motion measurement. Conclusions. Although proper motions cannot be used to confirm membership in σ Orionis, they can be instead used to discard a number of cluster member candidates without spectroscopy.

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“…However, much progress has been made in the last decade with the discovery of ever fainter, less massive members now reaching down to a few Jupiter masses in some nearby star-forming regions (e.g. Luhman 2007;Luhman et al 2009;Spezzi et al 2008;Bihain et al 2009;Boudreault & Bailer-Jones 2009;Scholz et al 2009;Haisch et al 2010;Geers et al 2011;Lodieu et al 2011, for some recent surveys). Much of the progress has come from dedicated surveys using wide-field instruments complemented by A&A 531, A33 (2011) Fig.…”

Section: Introductionmentioning

confidence: 99%

No substellar objects at the center of the Lupus 3 star-forming cloud

Comerón¹

2011

A&A

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Context. Current surveys of nearby star-forming regions and young aggregates that produce samples of objects spanning the entire mass range down to masses of a few Jupiter masses can address questions about differences in the substellar mass function among different regions and the lowest masses of objects that can form in isolation. Aims. Deep imaging of a selected area in the Lupus 3 star-forming region, characterized by a large number of known young stellar objects, has been carried out with the goal of producing a complete sampling of the mass function down to sub-Jupiter masses. Methods. I C JHK S imaging complemented with intermediate-band imaging sensitive to methane absorption has been obtained with the VLT. The observed area measures 7 3 × 7 4 (0.42 × 0.43 pc 2 at 200 pc) and the background is obscured by A V < 5 mag in approximately 70% of it. Detection limits (3σ) are I C = 25.6, J = 23.1, H = 22.3, and K S = 21.3. Cool objects with temperatures below 3000 K are identified by means of reddening-free indices. Objects cooler than ∼1300 K should also be detectable by comparing the flux in the H and methane-continuum bands.Results. The luminosities of the 17 identified cool objects are too low in all cases to be consistent with membership in the star-forming region. Their number agrees with the statistical expectation for the background population of very low-mass stars. A reexamination of known candidate young stellar objects leads to excluding eight of them, reducing the number of bona fide members in the area to 15, of which ten lie in low extinction regions. The expectation based on the stars-to-brown dwarf ratios derived in other young aggregates is to find two or three new brown dwarfs, whereas none have been found. The low-mass young stellar object Par-Lup3-3 is found to consist of two close components of similar brightness separated by 0 3. A very faint object is also detected 1 2 from the jet-driving very low-mass star Par-Lup3-4 that, if confirmed as a physical companion, would have an estimated mass of 1−2 M Jup . Conclusions. The absence of brown dwarfs in one of the most crowded areas of the Lupus 3 clouds, although limited by small-number statistics, argues against a mass function rich in very low-mass objects, as might have been expected if the apparent overabundance of mid-M spectral types in Lupus extended toward later types. The results also stress the importance of critically examining the actual nature of previously identified candidate young stellar objects at the time of drawing statistical conclusions about the substellar population.

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Candidate free-floating super-Jupiters in the young σ Orionis open cluster

Cited by 65 publications

References 65 publications

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

Stars and brown dwarfs in theσ Orionis cluster

No substellar objects at the center of the Lupus 3 star-forming cloud

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