Transcript IAU GA, Prague, Aug 2006 - Spanish Virtual Observatory

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
•
•
•
•
Introduction: BDs and VO.
Discovery of new candidates (field & SFR).
Characterization of SFR
Testing the BD formation theories.
IAU GA, Prague, Aug 2006
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 largearea 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
SDSS
DENIS
Courtesy
of SDSS
IAU GA, Prague, Aug 2006
BDs discovered using VO
 Filtering criteria: z & J-only
detections with z- J > 2.75
 SDSS: 15M obj.
 2MASS: 160M obj.
 300000 objects in common.
 However, systematic searches using a VO methodology
have not been performed so far.
IAU GA, Prague, Aug 2006
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
•
•
•
•
Introduction: BDs and VO.
Discovery of new candidates (field & SFR).
Characterization of SFR
Testing the BD formation theories.
IAU GA, Prague, Aug 2006
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.
 Simulations predict 12 L and 21 T dwarfs within the 10 pc
horizon, more than twice the number so far identified.
 2MASS/J 10σ-limit: 15.8
 DENIS/J 3σ-limit: 16.5
 2 < (z-J) < 4
 SDSS/z limit: 20.4
 The nearby T dwarf
population can be detected.
IAU GA, Prague, Aug 2006
…using a VO methodology
IAU GA, Prague, Aug 2006
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.
Discovering field BDs with 2MASS/SDSS
 Region surveyed:
 RA: 300° – 360° / DEC: 0° – 20°
 Three potential candidates, one of them already identified as BD
(2004, AJ, 127, 3553)
 Follow-up (IR imaging) foreseen for the coming weeks.
IAU GA, Prague, Aug 2006
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.
•The discovery of brown dwarfs cooler than T
dwarfs (the “Y” dwarfs) is one of the key science
drivers for UKIDSS.
IAU GA, Prague, Aug 2006
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
•
•
•
•
Introduction: BDs and VO.
Discovery of new candidates (field & SFR).
Characterization of SFR
Testing the BD formation theories.
IAU GA, Prague, Aug 2006
II.- Characterization of SFRs
The σ Orionis cluster
• 3 Ma, 360 pc, AV<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.
• Auxiliary data (IRAS, ROSAT)
 Identification of 5 CTTs.
IAU GA, Prague, Aug 2006
Characterization of SFRs (II)
 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.
IAU GA, Prague, Aug 2006
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
•
•
•
•
Introduction: BDs and VO.
Discovery of new candidates (field & SFR).
Characterization of SFR
Testing the BD formation theories.
IAU GA, Prague, Aug 2006
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.
•
•
•
•
•
•
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.
IAU GA, Prague, Aug 2006
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 06-07.
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