| Issue |
A&A
Volume 372, Number 1, June II 2001
|
|
|---|---|---|
| Page(s) | 173 - 194 | |
| Section | Interstellar and circumstellar matter | |
| DOI | https://doi.org/10.1051/0004-6361:20010474 | |
| Published online | 15 June 2001 | |
ISOCAM observations of the 
Ophiuchi cloud: Luminosity and
mass functions of the pre-main sequence embedded cluster *,**
1
Observatoire de Bordeaux, BP 89, 33270 Floirac, France
2
Stockholm Observatory, 133 36 Saltsjöbaden, Sweden
3
Service d'Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette, France
4
ESA/ESTEC, Astrophysics Division, The Netherlands
5
IAS, Université Paris XI, 91405 Orsay, France
6
ISO/SOC, Astrophysics Division of ESA, Villafranca, Spain
7
DESPA, Obs. Paris-Meudon, 5 Pl. J. Janssen, 92195 Meudon, France
8
JAC, 660 N. A'Ohoku Place, University Park, Hilo, HI 96720, USA
9
ENS Radioastronomie, 24 rue Lhomond, 75231 Paris, France
10
IAS, CNR, Area di Ricerca Tor Vergata, 00133 Roma, Italy
11
Observatoire de Lyon, 69230 Saint Genis Laval, France
Corresponding author: S. Bontemps, bontemps@observ.u-bordeaux.fr
Received:
9
May
2000
Accepted:
7
March
2001
We present the results of the first extensive
mid-infrared (IR) imaging survey
of the ρ Ophiuchi embedded cluster, performed
with the ISOCAM camera on board the ISO satellite.
The main ρ Ophiuchimolecular cloud L1688, as well as the two
secondary clouds L1689N and L1689S, have been completely surveyed
for point sources at 6.7 μm and 14.3 μm.
A total of 425 sources are detected in ~0.7 deg2, including
16 Class I, 123 Class II, and 77 Class III young stellar objects (YSOs).
Essentially all of the mid-IR sources coincide with near-IR
sources, but a large proportion of them are recognized for the first
time as YSOs. Our dual-wavelength survey allows us to identify essentially
all the YSOs with IR excess in the
embedded cluster down to 
~ 10-15 mJy.
It more than doubles the known population of Class II YSOs
and represents the most complete census to date of
newly formed stars in the ρ Ophiuchi central region.
There are, however, reasons to believe that several tens of
Class III YSOs remain to be identified below 
.
The mid-IR luminosities of most (~65% ) Class II objects are
consistent with emission from purely passive circumstellar disks.
The stellar luminosity function of the complete sample of Class II
YSOs is derived with good accuracy down to 
.
It is basically flat (in logarithmic units)
below 
, exhibits a possible local maximum at
,
and sharply falls off at higher luminosities.
A modeling of the luminosity function, using
available pre-main sequence tracks and plausible star formation histories,
allows us to derive the mass distribution of the Class II YSOs
which arguably reflects the initial mass function (IMF) of the
embedded cluster. After correction for the presence of unresolved binary systems,
we estimate that the IMF in ρ Ophiuchiis well described by a two-component
power law with a low-mass index of 
, a high-mass index of -1.7
(to be compared with the Salpeter value of -1.35), and a break
occurring at 
.
This IMF is flat with
no evidence for a low-mass cutoff down to at least ~
.
Key words: stars: formation / stars: low-mass, brown dwarfs / stars: luminosity function, mass function / stars: pre-main sequence / ISM: individual objects: ρ Ophiuchi cloud
© ESO, 2001
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