Virtual Observatory tools for the detection of T dwarfs. Enrique Solano, LAEFF / SVO Eduardo Martín, J.A. Caballero, IAC

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1 Virtual Observatory tools for the detection of T dwarfs Enrique Solano, LAEFF / SVO Eduardo Martín, J.A. Caballero, IAC

2 T dwarfs Low-mass (60-13 MJup), low-temperature (< K), low-luminosity brown dwarfs. Defining feature: presence of strong, broad methane absorption in the near-ir (H,K bands). Represent a class of objects linking the properties of observable low-mass stars and BD with the properties of unobservable extrasolar-planets. Gl229B N. Reid

3 Discovery criteria: proper motions The Calan-ESO survey Aim: find nearby stars. 14 ESO areas (5 x5 ) in the southern hemisphere. Proper motions were measured from plates taken 6-16yr apart. The Calan-ESO Proper-Motion Catalog contains 542 stars with proper motions 0.2"/yr (Ruiz et al., 2001,ApJS,133,119) All objects with proper motions exceeding Ruiz et al. (1997) 0.25/yr were selected for follow-up spectroscopy. Kelu-1 discovered at the plate limits (R ~ 19.5).

4 Large-area photometric surveys as discovery tools 2MASS: The 2-Micron All Sky Survey Carried out with two identical 1.3m. telescope (Mt Hopkins, Arizona and Cerro Tololo, Chile). 470M point sources + 1.6M extended sources.

5 2MASS as discovery tool 2MASS is ideal for identifying BD as the JHKs filters sample the peak of the SED It is possible to go relatively deep over the whole sky.

6 2MASS as discovery tool (II) WFTS: Wide-Field T Dwarf Search (Burgasser et al.2003, AJ): Searching since 1998 for T dwarfs using 2MASS point source catalogue. 74% of the sky covered. ~ 40 Brown Dwarfs identified.

7 Large-area surveys as discovery tools (II) SDSS: Sloan Digital Sky Survey Carried out with a dedicated 2.5m telescope on Apache Point Observatory (New Mexico). Courtesy of SDSS First operational phase, SDSS-I, ended in Jun In : More than 8,000 sq. deg. in five bandpasses, detecting nearly 200 million objects measuring spectra of more than 675,000 galaxies, 90,000 quasars, and 185,000 stars.

8 SDSS as discovery tool Although bluer than 2MASS, SDSS has proven to be very efficient in the finding of T dwarfs. No detection in u,g,r. i z>3 Sometimes only detection in the z band.

9 SDSS as discovery tool (II)

10 Large-area surveys as discovery tools (III) DENIS: Carried out with a 1m telescope (La Silla, ESO). Started in Operations completed on 9 Sept DENIS is a deep astronomical survey of the Southern Sky in I,J,Ks. 355M point sources covering square degrees.

11 Large-area surveys as discovery tools (III)

12 Is the color criteria enough?

13 The answer is NO

14 A lot of contamination Most of the detected objects are simply background (K-, M-type Main Sequence) stars.

15 What about late-type T dwarfs? The problem is not so severe but still remains. (J-H)<0.3; (H-K)<0.3 (Burgasser et al. 2002, ApJ) (J-H) 0.3 or (H-K) 0.0 (Burgasser et al. 2003, AJ).

16 Additional criteria: Optical/near IR colors T dwarfs are extremely red in the optical (R-J) > 9. Therefore, T dwarfs with J > (similar to Gliese 229B) would not appeared in optical sky surveys having typical limiting magnitudes of R < Candidates with optical counterparts in USNO within a few arcsec. of their 2MASS coordinates will be rejected.

17 GREAT!! but additional contaminants remain Minor planets have near-ir colours similar to T dwarfs and no optical counterpart due to motion. While catalogued minor planets are flagged by the 2MASS processing pipeline, uncatalogued minor planets or those with poorly determined orbits will not be identified. Removal of these objects requires second epoch imaging, typically in the IR. Burgasser et al. 2002, Apj

18 Discovering T dwarfs via methane imaging Filter system designed to highlight the strong absorption due to methane in the atmospheres of T dwarfs. Ellis et al. 2005, AJ

19 Our methodology 2MASS / DENIS crossmatching. DENIS (I,J,Ks). 355M objects. 2MASS (J,H,Ks). 471M objects. Good astrometric (0.5arcsec) and photometry accuracy. ( J=0.003, Ks=0.004) (Cabrera-Lavers & Garzón, 2003) The South also exists : most of the T dwarfs were discovered using 2MASS and/or SDSS.

20 Our workflow Proper motion: SELECT 2MASS sources NOT HAVING DENIS counterparts in 1.5 arcsec AND HAVING DENIS counterparts in 30 Photometry consistency: J(2MASS) J(DENIS) < 0.3 mag Good quality: Qflag(2MASS) = AA* Proper motion (II) < 10 arcsec/year Look for optical counterparts (filters B and R): if present then discarded.

21 Testing the method 68 T dwarf: - 32 not DENIS data MASS-DENIS < 1.5 arcsec. - Quality flags , ;pm:2.25; qflag: ABC , ; pm:1.15; qflag: ABU , ; pm:1.05; qflag:abu

22 The time baseline: a strong constraint 2MASS / North: Jun 1997 Feb MASS / South: Mar 1998 Feb 2001 DENIS: End 1995 Sep 2001 T dwarfs in davy/archive/)

23 The Virtual Observatory

24 A Virtual Observatory methodology

25 Selection criteria

26 Selection criteria

27 Cross-matching (I)

28 Cross-matching (II)

29 Cross-matching (III)

30 Filtering

31 Filtering (II) And now a second filter (pm < 10) and the optical cross-matching.

32 The search 620 sq. deg. DENIS: MASS:

33 The hope Qflag (2MASS) = AAB Quality J DENIS: 100/100 J-H = 0.8 H-K = 0.4

34 and the disappointment Observed at WHT: Prime Focus Imaging Camera. October 2005 A optical counterpart is seen in the 2MASS position. The optical magnitude is that expected from the 2MASS source. Conclusion: What we saw was: - A 2MASS background source - Too faint to be detected in DENIS - Nearby artifact in DENIS (which was supposed to be the DENIS counterpart of the 2MASS source). Object: , Limiting magnitudes: 2MASS DENIS: DENIS: 2MASS: J: ±0.096 J= ±0.22 i: J: H: K: H: ±0.080 K: ±0.126 Lesson learned: J2MASS below

35 Future projects Mass functions simulations by Burgasser (2001) predict 12 L and 21 T dwarfs, more than twice the number so far identified. This situation worsens dramatically if the substellar mass fuction is steeper. Solution: More systematic and complete surveys. but some of them will be too faint to be detected and will remain to be uncovered by future surveys.

36 Systematic searches 2MASS-DENIS: Carry on with the global search 2MASS-DENIS: Searches in selected/young regions. 2MASS-SDSS: Exploit DR4 (2005) 180M vs 141 M objects

37 Exploitation of new surveys

38 The solar neighbourhood is poorly known. The situation is even worse at substellar masses because of their intrinsic faintness. Early 2005

39 Variability 2MASS multi-epoch photometry gives some hint of photometric variability. Probably intrinsic due to the motion and evolution of patchy condensate clouds in the upper atmospheres of early and mid type T dwafrs (Burgasser et al 2003). This must be considered carefully as the 2MASS J-filter bandpass extend well into the 1.4 microb telluric H20 band.

40 Background info Distance estimates can be made using the spectral type, 2MASS photometry and the absolute magnitudes of T dwarfs with measured parallaxes. Examination of the low-resolution spectra indicate that the majority of these candidate sources are late-type M dwarfs, based on the presence of weak H2O absorption at 1.4 and 1.9 µm; CO absorption at 2.3 µm; TiO and VO bands at µm; and FeH, Na I, and K I absorption at J-band. The data were taken from scans of 7,435 Schmidt plates taken from various sky surveys during the last 50 years. (USNO)

41 The solar neighbourhood is poorly known.

42 Discovery criteria: proper motions (II) SuperCOSMOS Sky Survey (SSS) a scan of the entire southern sky made from plates in Bj,R,I. ε Indi B: T2.5, d=3.6 pc (one of the nearest BD), pm:4.7arcsec/year, SSS: I < 17, No R, No Bj The output then examined with 2MASS. (Scholz et al. 2003, A&A 398,L29)