Brown dwarfs and star forming regions in the framework of the Virtual Observatory. Enrique Solano, LAEFF / SVO Eduardo Martín, IAC / SVO Network J. A. Caballero, MPI / SVO Network IAU GA, Prague, Aug 2006 Introduction: BDs and VO. Discovery of new candidates (field & SFR). Discovery of new candidates (field & SFR). Characterization of SFR Characterization of SFR Testing the BD formation theories. Testing the BD formation theories.

The search for the rare  The advances in technology (large-scale detector arrays, computing capability, highly automated pipelines and analysis software,…) have undergone an explosion of productivity in the search for rare objects through large- area surveys. From the brightest and most distant quasars (e.g Fan et al. 2004)… … to the faintest and nearest stars and brown dwarfs (e.g. Burgasser et al. 2002)  The Virtual Observatory goes a step ahead offering The possibility of joining these large data sets The development of tools to facilitate the efficient analysis of the contents. IAU GA, Prague, Aug 2006

Brown dwarfs  Represent a class of objects linking the properties of observable low-mass stars and BD with the properties of unobservable extrasolar-planets. IAU GA, Prague, Aug 2006

Brown dwarfs: detection methods  Most of them have been identified using Large-area, optical and near-IR surveys Color criteria 2MASS Courtesy of SDSS SDSSDENIS IAU GA, Prague, Aug 2006

BDs discovered using VO IAU GA, Prague, Aug 2006  Filtering criteria: z & J-only detections with z- J > 2.75  SDSS: 15M obj.  2MASS: 160M obj.  objects in common. However, systematic searches using a VO methodology have not been performed so far. However, systematic searches using a VO methodology have not been performed so far.

Brown dwarfs and star forming regions in the framework of the Virtual Observatory. Enrique Solano, LAEFF / SVO Eduardo Martín, IAC / SVO Network J. A. Caballero, MPI / SVO Network IAU GA, Prague, Aug 2006 Introduction: BDs and VO. Discovery of new candidates (field & SFR). Discovery of new candidates (field & SFR). Characterization of SFR Characterization of SFR Testing the BD formation theories. Testing the BD formation theories.

I.- Discovering field BDs with 2MASS/DENIS/SDSS … DENIS, 2MASS, SDSS/DR5: Millions of objects and still new releases to come. (SDSS/DR5 a few months ago). “The South also exists”: most of the T dwarfs were discovered using 2MASS / SDSS  DENIS exploitation. Good astrometric (0”.5arcsec) and photometry accuracy. IAU GA, Prague, Aug MASS/J 10σ-limit: 15.8 DENIS/J 3σ-limit: < (z-J) < 4 SDSS/z limit: 20.4  The nearby T dwarf population can be detected. Simulations predict 12 L and 21 T dwarfs within the 10 pc horizon, more than twice the number so far identified.

…using a VO methodology IAU GA, Prague, Aug 2006

Discovering field BDs with 2MASS/SDSS IAU GA, Prague, Aug 2006  Region surveyed: RA: 300° – 360° / DEC: 0° – 20°  Three potential candidates  Three potential candidates, one of them already identified as BD (2004, AJ, 127, 3553)  Follow-up (IR imaging) foreseen for the coming weeks. Discovering field BDs with 2MASS/DENIS  Region surveyed: RA: 300° – 360° / DEC: -10° / -34° RA: 210° – 270° / DEC: -1° / -13°  10+8 potential candidates  Follow-up (IR imaging) already done. Analysis on-going.

What’s next? IAU GA, Prague, Aug 2006

UKIDSS (II) z (SDSS) limiting magnitude: 20.4 J (2MASS) limiting magnitude: 15.8  Faint SDSS sources do not have 2MASS counterparts. IAU GA, Prague, Aug 2006 The discovery of brown dwarfs cooler than T dwarfs (the “Y” dwarfs) is one of the key science drivers for UKIDSS.The discovery of brown dwarfs cooler than T dwarfs (the “Y” dwarfs) is one of the key science drivers for UKIDSS.

Brown dwarfs and star forming regions in the framework of the Virtual Observatory. Enrique Solano, LAEFF / SVO Eduardo Martín, IAC / SVO Network J. A. Caballero, MPI / SVO Network IAU GA, Prague, Aug 2006 Introduction: BDs and VO. Discovery of new candidates (field & SFR). Discovery of new candidates (field & SFR). Characterization of SFR Characterization of SFR Testing the BD formation theories. Testing the BD formation theories.

II.- Characterization of SFRs IAU GA, Prague, Aug 2006 The σ Orionis cluster 3 Ma, 360 pc, A V <1 mag Tycho- 2MASS corr. 30 arcmin search radius. ~ 40 stars Membership on the basis of proper motions and color-magnitude diagram (Tycho2-2MASS corr.) Cluster mass function from 25 to 2 solar masses.  Cluster mass function from 25 to 2 solar masses. Identification of 5 CTTs. Auxiliary data (IRAS, ROSAT)  Identification of 5 CTTs.

Characterization of SFRs (II) IAU GA, Prague, Aug 2006  Jumping to the substellar regime: From 3 to 0.05 solar masses 2MASS / DENIS correlation. 30 arcmin search radius. Selection criteria based on well-known cluster members.  On-going: Similar analysis for all the clusters of the Orion belt.

Brown dwarfs and star forming regions in the framework of the Virtual Observatory. Enrique Solano, LAEFF / SVO Eduardo Martín, IAC / SVO Network J. A. Caballero, MPI / SVO Network IAU GA, Prague, Aug 2006 Introduction: BDs and VO. Discovery of new candidates (field & SFR). Discovery of new candidates (field & SFR). Characterization of SFR Characterization of SFR Testing the BD formation theories. Testing the BD formation theories.

Testing the BD formation theories The way how BDs are formed is still a matter of debate.  Their masses are two orders of magnitude smaller than the average Jeans mass (approximate estimate of the lower limit to the stellar mass given a density and temperature) in star-forming clouds. BUT …  They are as numerous as “normal” stars. IAU GA, Prague, Aug 2006

The project: rationale So far, all the surveys for young BDs concentrate on the known star-formation regions (e.g Taurus-Auriga). Depending on the ejection velocity BDs may have travelled far from their birth sites and not revealed by the previously mentioned surveys. Check the ejection model by cross-correlating IPHAS and 2MASS to search young BD by their Hα emission and IR colors. IAU GA, Prague, Aug 2006 IPHAS INT Photometric Hα survey (Drew’05) 1800 deg² -5<b<+5 r’, i’, H filters r’=20 (10 ), i’~19 80M sources in the Final Catalogue.

The project: candidates and follow up Filtering using appropriate (r- Hα), (I-J), (J-H), (H-K) color criteria. (~ 300 candidates) Low resolution spectroscopic follow-up for a proper identification and determination of physical parameters. WHT: 2 nights (Aug 1st-2nd). 35 candidates observed. NOT/ALFOSC: 5 nights granted in Winter IAU GA, Prague, Aug 2006

Conclusions The scarcity in the number of known brown dwarfs has a considerable impact on different fields of Astrophysics, in particular on the area of star formation. This problem has been identified as a key VO-Science case both by AstroGrid (included in the "Top-Ten" cases) and EURO-VO (through its Science Reference Mission). Building a census of substellar objects implies the discovery of a statistically significant number of them through queries that combine attributes available from different archives. This is an approach out of the scope of the "classical" methodology but that perfectly fits into the Virtual Observatory. The goal of this presentation has been to demonstrate the potential of carrying out this type of analysis in the VO framework. IAU GA, Prague, Aug 2006

The observational evidences A high percentage of BDs found in Star Forming Regions show IR excesses  Existence of disks. IAU GA, Prague, Aug 2006 (1 Myr) (~5 Myr) Hα double peak  Indicator of accretion. Scenario compatible with a disk dissipation in a timescale similar to T Tauris.

The theories: IAU GA, Prague, Aug 2006 Photoerosion of prestellar cores (Whitworth & Zinnecker, 2004): Turbulent fragmentation (Padoan & Nordlund, 2004) Ejection (Reipurth & Clarke, 2001)