Efficient identification of cool stars and brown dwarfs with solar and sub-solar abundances using Virtual Observatory tools.

E. Solano¹, M. Aberasturi¹, N. Lodieu2,3, M. Gálvez-Ortiz¹, J.A. Caballero¹, E. L. Martín¹, M. Espinoza Contreras², M.R. Zapatero-Osorio¹, B. Montesinos¹

1.- Centro de Astrobiología (INTA-CSIC), Madrid, Spain; 2.- Instituto de Astrofísica de Canarias (IAC), La Laguna, Tenerife, Spain; 3.- Universidad de La Laguna (ULL), Tenerife, Spain.

Cool subdwarfs (sds)

Introduction

Metal-poor dwarfs showing halo kinematics. Useful tracers of the Galactic chemical history. Aim: Build a complete census of ultracool subdwarfs and expand the low-metallicity classification into the L and T regimes. Methodology:

– Cross-matching: SDSS(DR7) vs UKIDSS LAS (DR5).

– Photometric and proper motion criteria (Figs 1,2).

Results:

– 20 new sdM/sdL with spectral types later than M5 confirmed spectroscopically, including 2 early L-subdwarfs within 100 pc.

– Previously <60 sdMs, 7 sdLs.

– 60% rate success (up to 90% once errors in SDSS positions are properly handled).

– New searches on-going.

Brown dwarfs (BDs)

Massive optical and infrared imaging surveys are the main contributors to the discovery of brown dwarfs. Aim: Demonstrate that VO tools are efficient in identifying and characterizing brown dwarfs. Methodology:

– Cross-matching: WISE(Prelim. Release) vs 2MASS (PSC) and SDSS (DR7).

– Photometric and proper motion criteria (Fig 4).

Results:

– 31 BDs were identified. 25 already known and 6 candidates not previously reported in the literature.

– Effective temperatures were obtained using VOSA (Bayo et al. 2008 A&A, 492, 277B from the SED fitting between observed photometry and a suite of collections of theoretical models (Fig. 5).

– Distances derived from absolute magnitude – spectral type relations.

– New searches on-going.

Figure 4. Colour- colour diagram of our six candidates (solid circles) compared with a sample of known L and T dwarfs observed with WISE.

Figure 5. VOSA SED fitting for our six BD candidates. Catalogue and synthetic photometry are represented in red and blue, respectively. Points not considered in the fitting are shown in black.

Wide, very low-mass (VLM) multiple systemsResults:

– 12 new wide, VLM multiple systems (Fig. 3).

– Physical association confirmed through common proper motion, distance, age and low probability of chance alignment.

– Young ages, which favours the existence of weakly bound systems (less probability of being gravitationally perturbed by passing stars and/or molecular clouds).

– Gálvez-Ortiz et al.: To be submitted soon.

– New searches foreseen.

Multiple systems are key elements to understand the formation and evolution of very-low mass objects. Wide (projected physical separations > 100 AU) systems are rare and searches remain largely incomplete. Aim: Use VO tools to discover wide, VLM systems in large areas of the sky. Methodology:

– Cross-matching: 2MASS (PSC) vs SDSS (DR7). GLIMPSE vs 2MASS (PSC)

– Photometric & proper motion criteria.

Figure 3.Finding charts (SDSS images) of some of the wide, VLM systems found in our search. Primaries (defined as the brightest objects in the J band) are marked with an arrow. B,C components are marked with crosses and circles, respectively.

Nearby M dwarfs

The frequency of M dwarfs in the Galaxy, combined with their small masses and radii make M dwarfs excellent targets to detect terrestrial planets. Aim: Increase the number of known, nearby M dwarfs. Methodology:

– Cross-matching: CM14 and 2MASS (PSC).

– Photometric criteria only.

– Bright objects (J< 10.5).

Identification of low mass stars and brown dwarfs (M < 0.075M0) can be made by using a combination of data (colours, proper motions,...) available from different resources distributed worlwide.

Very time-consuming tasks if performed by hand but, on the contrary, efficiently carried out in the framework of the Virtual Observatory (VO).

The Virtual Observatory Main goal: Guarantees an easy and efficient access and analysis of the information hosted in astronomical archives.VO is already a working research infrastructure (over 70 VO-papers since 2009).

The Spanish VO (SVO)Member of the International Virtual Observatory Alliance (IVOA) since 2004. Coordination of the VO activities at national level.

Major line of work: Collaborations with groups whose science cases can benefit from using a VO methodology → THIS POSTER.

Very productive: A third of the refereed VO-papers include SVO authors.

The VO-tools Major features: Discovery, gathering and analysis of distributed information taking advantage of the VO standards. Much easier for the user.

Figure 2. Location in a reduced proper motion diagram of our new ultracool subdwarfs (filled symbols) as well as known sds from the literature (open symbols).

Results:

– 16 new, bright M dwarfs were identified and confirmed spectroscopically (Fig.6). Three Taurus members, one with clear signposts of accretion (Fig. 7).

– A new M dwarf locus has been identified in the reduced proper motion diagram.

– Work on-going.

Figure 7. Hα EWs as a function of spectral type. The empirical border between activity and accretion (Barrado y Navascués & Martín 2003 AJ,126,2997) is shown. M5.5 is the spectral type used to define the substellar-mass limit at 100 Myr.

Figure 6. Spectra of some of our candidates (red) compared to reference stars (blue.)

Figure 1. Colour- colour diagram showing the position of known subdwarfs with respect to the solar-metallicity M/L dwarf sequence (0= M0; 5=M5; 10=L0,...).