Protoplanetary discs of isolated VLMOs discovered in the IPHAS survey

Transcription

1 Protoplanetary discs of isolated VLMOs discovered in the IPHAS survey Luisa Valdivielso Casas Collaborators: E. Martín, H. Bouy, E. Solano,J. Drew,R. Greimel 1 IAC - ULL 14 de septiembre 2010

2 Outline Introduction Objectives of this work VLMOs search Conclusions 2

3 Introduction Very low mass stars and brown dwarfs - DETECTION Very few brown dwarfs candidates were observed prior to 2MASS, SDSS, & other surveys in the mid 1990 s (large-area, optical and near-ir surveys) First brown dwarf discoveries in 1995 (Rebolo et al. 1995, Nakajima et al. 1995) Lithium test: - Confirm the substellar nature of an object - Youth feature 3

4 Introduction Very low mass stars and brown dwarfs - DETECTION Many young objects show Hα emission due to accretion processes. association with circumstellar discs Broadband optical surveys have missed strong Hα emitters as they appear bluer than they are. Search in star formation regions such as Chamaeleon, ρoph, σorionis, Serpens, Taurus, Trapezium 4

5 Introduction: IPHAS Survey Observations with WFC (Wide Field Camera) on Isaac Newton Telescope, a mosaic of 4 EEV2kx4k CCDs, pixel size 0.33, f.o.v. ~0.25 degs Filters: r (6240 Å), i (7743 Å) Sloan, Hα (6568/95 Å) Magnitude limit r ~22 (5σ) Area: 1800º 2 in the North of the Milky Way r i Photometric catalogue of 80 million objects Detection of ~20000 Hα emitting objects Hα Drew et al

6 Outline Introduction Objectives of this work VLMOs search Conclusions 6

7 Objectives of this work Sistematic search of young very low-mass objects with accretion discs over a large sample (IPHAS Survey) Help to improve our understanding of the main formation mechanisms of low-mass objects (not well understood yet) Feasible: Low-mass objects are more luminous when they are young. Young sub-stellar objects are as numerous as stars. They occur both in the field (single or binary), and in star forming regions. 7

8 Outline Introduction Objectives of this work VLMOs search Data selection & observations Results Conclusions 8

9 VLMO Data: targets selection Cross-match of IPHAS with 2MASS (within 1 ) using Aladin - Available photometry: r, i, Hα, J, H, K s 2MASS sources: a) 0.7<J-H<1.3 b) 0.4<H-K s <1.1 s unreddened main sequence M6 giants IPHAS counterparts: subgiants M0 1.1<r -Hα<3.0 K candidates for spectroscopic follow-up A0 Drew et al

10 WHT/ISIS: VLMO Data: Spectroscopic Observations - 2 nights, 35 targets - texp : s - R158R (1.63 Å /pixel) grating in red arm slit NOT/ALFOSC: - 5 nights, 53 targets - texp : s - Grism 5 (3.1 Å /pixel) -1 slit 3m-Shane Telescope/KAST: - 4 nights, 25 targets -texp : s - Gratings : 300/7500(4.6Å/pixel) 600/7500(2.3Å/pixel) - 2 slit 113 spectra (out of 2251 candidates) 10

11 Results 113 IPHAS targets observed (5%): 48 real candidates according new IPHAS photometry new catalogue with final IPHAS calibration 42 objects show strong Hαα emission (success rate > 80%) 33 M SpT with negligible reddening (visual inspection) Valdivielso et al

12 Results: Color-color diagrams New IPHAS photometry s observed Hα, <M4 Hα, >M4 Valdivielso et al

13 Results 113 IPHAS targets observed (5%): 48 real candidates according new IPHAS photometry new catalogue with final IPHAS calibration 42 objects show strong Hαα emission (success rate > 80%) 33 M SpT with negligible reddening (visual inspection) Valdivielso et al

14 Results: Hα vs SpT Barrado y Navascués & Martín (2003) criteria to study the accretion level of the targets. All objects with Hα emission show accretion! Valdivielso et al

15 Results: NaI doublet measurements NaI doublet equivalent width measurements between 8172Å and 8207Å NaI logg Comparison with field M dwarfs & Upper Sco members (5Myr) Later type objects show lower surface gravity Confirmation of VLMOs being young and under formation! W(NaI) Valdivielso et al M-SpT Upper-Sco 15

16 Results: A new IPHAS VLMO catalogue New catalogue based on the improved photometry and improved selection criteria for selecting very young BDs List of 1646 candidates: 10 known in Simbad ( IR sources,1 Mira Cep Star) 1 previously selected as YSO candidate 1636 new objects ~1300 very young BDs (~150 found in young stellar clusters, MoC and SFRs) 16

17 Results: Spectro-photometric distances Where are these newly discovered VLMOs? Search for parent associations. To do this: 1. Baraffe Nextgen models log g=4 ; age 2Myr and 5Myr to compute distances Av estimation, SpT refinement 2. SIMBAD search within 30 arcmin 17

18 Results: Spectro-photometric distances Results 27 objects located near molecular clouds, star formation regions and young open clusters: Serpens, North American Nebula, Cep IV, IC1396, Cygnus 3 previously reported as YSO candidate, 1 new object detected Some objects are far away from any known young association within 30 arcmin. 2 isolated objects (nothing within 30 arcmin) Free-floating ejected from SFR? Members of unknown nearby associations? (Open question ) 18

19 Results: Spectral Energy Distributions Search Spitzer data to compute SED s Data avaliable for 17 objects 9 objects with µm All SEDs compatible with having accretion discs! Valdivielso et al. 2010b (submitted) 19

20 VLMOs search: Summary Search young low mass objects on the IPHAS survey Spectral type (SpT) classification with low resolution spectroscopy of the targets Study the chromospheric/accretion activity measuring the Hα equivalent width NaI doublet (818.3nm, 819.5nm) equivalent width measurements as surface gravity indicator Distance estimation and comparison with known SFR s Spitzer photometry, SED s New young BDs catalogue 93% IPHAS survey 20

21 Outline Introduction Objectives of this work VLMOs search Conclusions 21

22 CONCLUSIONS VLMOs search 1. VO tools are very efficient to search for very low mass stars and brown dwarfs using large databases. 2. It has been demonstrated that accreting VLM stars and young BDs can be successfully identified in IPHAS. Full exploitation of the IPHAS database and a future extension of it in the southern hemisphere will be crucial in identifying VLM accreting objects near to and far from well-known starforming regions. 3. It has been confirmed that most of the objects with Hα emission show evidences of accretion processes and very low surface density, with ages younger than 5Myr. 4. Spitzer data show infrared excesses. This confirms the existence of protoplanetary discs. 22

23 CONCLUSIONS VLMOs search 5. VLMOs have been detected spectroscopically in different regions which had not been investigated before. Some targets could be the first known evidence of stellar formation in those regions. 6. Two isolated objects have been discovered. These objects show the same properties of those observed in the cores of SFRs, molecular clouds or young open clusters (spectral features and colors). 7. ~ young BDs could be detected in the new improved catalogue, and tentative estimations show that at least 100 very young isolated BDs could be discovered. By studying their properties, new constraints on the formation theories of such objects could be found. 23