New VLM Members of Southern Star Forming Regions
B. López Martí
Martí(1), J. Eislö
Eislöffel(2), R. Mundt(3) & A. Scholz(2)
(1) Departament d’Astronomia i Meteorologia,Universitat de Barcelona, E-08028 Barcelona, Spain
(2) Thüringer Landessternwarte, D-07778 Tautenburg, Germany
(3) Max Planck Institut für Astronomie, D-69117 Heidelberg, Germany
Identification of Young Very Low-Mass Objects
with WFI Imaging Observations
Chamaeleon I: 44 stars, 28 brown dwarf candidates
Estimated age: 3 Myr
Estimated distance: 160 pc
1. Select candidates in a (I, R-I) colourmagnitude diagram:
Suitable candidates are red and faint,
and spread around a cloud isochrone.
2. Select probable members in a (Hα, Hα-R) colour-magnitude diagram:
A blue Hα-R colour indicates Hα emission (right panel), since it is related to the Hα
equivalent width (left panel).
Ha Emission No Ha Emission
Surveyed area: ~1.2 •º
The found objects are placed around and
between the two intermediate-mass stars, near
the cloud cores (right figure). It seems thus
unlikely that they have been ejected from their
birth sites.
Completing our sample with previously known
objects (Gauvin & Strom 1992; Comerón et al.
2000), a value of the index α of the mass
function could be estimated:
dN/dM=M- α , α =0.6±0.1
This value is consistent with those obtained in
other star forming regions and young clusters.
3. Estimate spectral types using a (M855-M915) colour-magnitude diagram:
Correlation between spectral types and M855-M915 colour
(only valid for spectral types >M4)
M855
(855/20)
M915
(915/28)
Near-infrared observations (Kenyon & Gómez 2001; DENIS) and ISOCAM midinfrared data (Persi et al. 2000) show that some of these objects have infrared
excesses, indicating that their Hα emission is probably due to accretion from a
circum(sub)stellar disk.
Spectrum of a M-type object.
The M855 filter lies on the region where the
characteristic TiO and VO absorption bands appear.
The M9155 filter lies on a pseudocontinuum region.
Chamaeleon II: No brown dwarfs?
Estimated age: 1 Myr
Estimated distance: 180 pc
Surveyed area: ~0.3 •º
4. Use public near- and mid-infrared data to confirm the identifications.
Lupus 3: 16 VLM stars, 7 brown dwarf candidates
Estimated age: 1-5 Myr Estimated distance: 140-200 pc Surveyed area: ~1.6 •º
Stars (yellow points) and brown dwarf
candidates (red points) are found near
the dark strip of the main cloud core
(left figure) .
Only one candidate seems to have Hα emission (left panel).
Its position in the 2MASS (J-H, H-K) diagram (right panel) corresponds to that of a
young VLM star according to the models (red lines, Baraffe et al. 1998), but it could
also be a slightly extincted background dwarf (blue lines, Bessell & Brett 1988).
This result can be interpreted in terms of the properties of this region, which is
younger than the other two and contains more embedded than visual objects.
Most of the objects found are M5 stars
(red histogram in upper right panel),
consistent with the properties of the
total population (magenta histogram:
objects from Hughes et al. 1994,
Comerón et al. 2003 and this work).
Only one brown dwarf candidate is
found to have a clear near-infrared
excess according to 2MASS data
(lower right panel), but, due to its
faintness, Hα emission could not be
confirmed with our photometry.
References:
Baraffe, I., Chabrier, G., Allard, F. & Hauschildt, P.H. 1998, A&A 337, 403
"
Bessell, M.S. & Brett, J.M. 1988, PASP 100, 1134
Comerón, F., Neuhäuser, R. & Kaas, A.A. 2000, A&A 359, 269
Comerón, F., Fernández, M., Baraffe, I. et al. 2003, A&A 406, 269
Gauvin, L.S. & Strom, K.M. 1992, ApJ 385, 217
Hughes, J.D., Hartigan, P., Krautter, J. & Kelemen, J. 1994, AJ 108, 1071
Kenyon, S.J. & Gómez, M. 2001, AJ 121, 2673
López Martí, B. 2003, PhD Thesis
López Martí, B., Eislöffel J., Scholz, A. & Mundt, R. 2004, A&A 416, 555
Persi P., Marenzi, A.R., Olofsson, G. et al. 2000, A&A 357, 219
2MASS data from the NASA/IPAC Infrared Science Archive (http://irsa.ipac.caltech.edu)
“The Many Scales in the Universe”, Joint European and National Astronomical Meeting (JENAM), Granada (Spain), September 2004
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