203 research outputs found
The Eagle's EGGs: fertile or sterile?
We present a deep, high spatial resolution (0.35 arcsec FWHM), near-infrared (1-2.5 micron) imaging survey of the Eagle Nebula, M16, made with the VLT, centred on the famous elephant trunks. We compare these data with the existing HST optical images to search for evidence of ongoing or recent star formation in the trunks, and in particular in the 73 small evaporating gaseous globules (EGGs) on their surface. We find that two of the three HST trunks have relatively massive YSOs in their tips. Most of the EGGs appear to be empty, but some 15% of them do show evidence for associated young low-mass stars or brown dwarfs: in particular, there is a small cluster of such sources seen at the head of the largest trunk
Are there brown dwarfs in globular clusters?
We present an analytical method for constraining the substellar initial mass
function in globular clusters, based on the observed frequency of transit
events. Globular clusters typically have very high stellar densities where
close encounters are relatively common, and thus tidal capture can occur to
form close binary systems. Encounters between main sequence stars and
lower-mass objects can result in tidal capture if the mass ratio is > 0.01. If
brown dwarfs exist in significant numbers, they too will be found in close
binaries, and some fraction of their number should be revealed as they transit
their stellar companions. We calculate the rate of tidal capture of brown
dwarfs in both segregated and unsegregated clusters, and find that the tidal
capture is more likely to occur over an initial relaxation time before
equipartition occurs. The lack of any such transits in recent HST monitoring of
47 Tuc implies an upper limit on the frequency of brown dwarfs (< 15 % relative
to stars) which is significantly below that measured in the galactic field and
young clusters.Comment: MNRAS in pres
Spectroscopic classification of red high proper motion objects in the Southern Sky
We present the results of spectroscopic follow-up observations for a sample
of 71 red objects with high proper motions in the range 0.08-1.14 arcsec/yr as
detected using APM and SSS measurements of multi-epoch photographic Schmidt
plates. Red objects were selected by combining the photographic BjRI magnitudes
with 2MASS near-infrared JHKs magnitudes. Some 50 of the 71 spectroscopically
classified objects turn out to be late-type (>M6) dwarfs and in more detail,
the sample includes 35 ultracool dwarfs with spectral types between M8 and L2,
some previously reported, as well as five M-type subdwarfs, including a cool
esdM6 object, SSSPM J0500-5406. Distance estimates based on the spectral types
and 2MASS J magnitudes place almost all of the late-type (>M6) dwarfs within 50
pc, with 25 objects located inside the 25 pc limit of the catalogue of nearby
stars. Most of the early-type M dwarfs are located at larger distances of
100-200 pc, suggesting halo kinematics for some of them. All objects with
Halpha equivalent widths larger than 10 Angstroms have relatively small
tangential velocities (<50 km/s). Finally, some late-type but blue objects are
candidate binaries.Comment: accepted on 06 June 2005 for publication in A&A, 22 pages, 14
figures, 7 table
SSSPM J1444-2019: an extremely high proper motion, ultracool subdwarf
We present the discovery of a new extreme high proper motion object (3.5
arcsec/year) which we classify as an ultracool subdwarf with [M/H] = -0.5. It
has a formal spectral type of sdM9 but also shows L-type features: while the VO
bands are completely absent, it exhibits extremely strong TiO absorption in its
optical spectrum. With a radial velocity of about -160 km/s and a rough
distance estimate of 16--24 pc, it is likely one of the nearest halo members
crossing the Solar neighbourhood with a heliocentric space velocity of
(U,V,W)=(-244,-256,-100)+/-(32,77,6) km/s.Comment: 4 pages, 4 figures (Fig.1a-d available as jpg files), accepted for
publication in Astronomy & Astrophysics Letter
Recommended from our members
Intense molecular emission from the Lagoon nebula, M8
The discovery is reported of the second strongest source of mm and submm wavelength CO line emission, towards M8, the Lagoon Nebula in Sagittarius. The ~31 M⊙ molecular core has dimensions ~0.2 x 0.3pc and is centred on the O7V star Herschel 36 (H36), near the Hourglass Nebula in the core of M8. Emission from the CO line wings extends to the north and south of the Hourglass, although a lack of near-IR H2 emission indicates that outflow activity is much less prominent than in many active star-formation regions, and suggests that the CO line wings may trace the expanding edge of a cavity around H36. The molecular line data are compared with new near-IR narrow-band, continuum-subtracted images in He I, H2, and H,+ (Brγ) lines and archival HST emission-line images in Hα, [O III], and [S II]. The optical and near-IR data are found to be broadly consistent with previous photo-ionisation models of the Hourglass, which is excited by H 36. However, there are variations in the He I/Brγ line ratio which are difficult to explain
Deep ROSAT Surveys & the contribution of AGNs to the soft X-ray background
The ROSAT Deep Surveys in the Lockman Hole have revealed that AGNs are the main contributors (~75%) to the soft X-ray background in the 1–2 keV band. Using new optical/infrared and radio observations we have obtained a nearly complete identification (93%) of the 91 X-ray sources down to a limiting flux of 1.2·10^(–15) erg cm^(–2) s^(–1) in the 0.5–2.0 keV band. We present the optical colors and the emission line properties of our AGNs in comparison with other X-ray selected AGN samples. Furthermore we discuss the fraction of red AGNs found in the ROSAT Deep Surveys. From the ROSAT Deep Surveys we see no evidence for a new class of X-ray bright galaxies, which significantly contributes to the soft X-ray background
A highly-collimated SiO jet in the HH212 protostellar outflow
We mapped the HH212 Class 0 outflow in SiO(2--1, 5--4) and continuum using
the PdBI in its extended configurations. The unprecedented angular resolution
(down to 0.34") allows accurate comparison with a new, deep H2 image obtained
at the VLT. The SiO emission is confined to a highly-collimated bipolar jet
(width 0.35") along the outflow axis. The jet can be traced down to within 500
AU of the protostar, in a region that is heavily obscured in H2 images. Where
both species are detected, SiO shows the same overall kinematics and structure
as H2, indicating that both molecules are tracing the same material. We find
that the high-velocity SiO gas near the protostar is not tracing a wide-angle
wind but is already confined to a flow inside a narrow cone of half-opening
angle < 6 deg.Comment: Astronomy and Astrophysics Letter, in pres
- …