406 research outputs found
An Unbiased 1.3 mm Emission Line Survey of the Protoplanetary Disk Orbiting LkCa 15
The outer (>30 AU) regions of the dusty circumstellar disk orbiting the ~2-5
Myr-old, actively accreting solar analog LkCa 15 are known to be chemically
rich, and the inner disk may host a young protoplanet within its central
cavity. To obtain a complete census of the brightest molecular line emission
emanating from the LkCa 15 disk over the 210-270 GHz (1.4 - 1.1 mm) range, we
have conducted an unbiased radio spectroscopic survey with the Institute de
Radioastronomie Millimetrique (IRAM) 30 meter telescope. The survey
demonstrates that, in this spectral region, the most readily detectable lines
are those of CO and its isotopologues 13CO and C18O, as well as HCO+, HCN, CN,
C2H, CS, and H2CO. All of these species had been previously detected in the
LkCa 15 disk; however, the present survey includes the first complete coverage
of the CN (2-1) and C2H (3-2) hyperfine complexes. Modeling of these emission
complexes indicates that the CN and C2H either reside in the coldest regions of
the disk or are subthermally excited, and that their abundances are enhanced
relative to molecular clouds and young stellar object environments. These
results highlight the value of unbiased single-dish line surveys in guiding
future high resolution interferometric imaging of disks.Comment: 35 pages, 9 figures, accepted for publication in The Astrophysical
Journa
The HARPS search for southern extra-solar planets XXXII. Only 4 planets in the Gl~581 system
The Gl 581 planetary system has generated wide interest, because its 4
planets include both the lowest mass planet known around a main sequence star
other than the Sun and the first super-Earth planet in the habitable zone of
its star. A recent paper announced the possible discovery of two additional
super-Earth planets in that system, one of which would be in the middle of the
habitable zone of Gl 581. The statistical significance of those two discoveries
has, however, been questioned. We have obtained 121 new radial velocity
measurements of Gl 581 with the HARPS spectrograph on the ESO 3.6 m telescope,
and analyse those together with our previous 119 measurements of that star to
examine these potential additional planets. We find that neither is likely to
exist with their proposed parameters. We also obtained photometric observations
with the 2.5 m Isaac Newton Telescope during a potential transit of the inner
planet, Gl 581e, which had a 5% geometric transit probability. Those
observations exclude transits for planet densities under 4 times the Earth
density within -0.2 sigma to +2.7 sigma of the predicted transit center.Comment: Submitted to Astronomy & Astrophysic
The HARPS search for southern extra-solar planets XLI. A dozen planets around the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628, and GJ 3293
Context. Low mass stars are currently the best targets for searches for rocky
planets in the habitable zone of their host star. Over the last 13 years,
precise radial velocities measured with the HARPS spectrograph have identified
over a dozen super-Earths and Earth-mass planets (msin i<10Mearth ) around M
dwarfs, with a well understood selection function. This well defined sample
informs on their frequency of occurrence and on the distribution of their
orbital parameters, and therefore already constrains our understanding of
planetary formation. The subset of these low-mass planets that were found
within the habitable zone of their host star also provide prized targets for
future atmospheric biomarkers searches. Aims. We are working to extend this
planetary sample to lower masses and longer periods through dense and long-term
monitoring of the radial velocity of a small M dwarf sample. Methods. We
obtained large numbers of HARPS spectra for the M dwarfs GJ 3138, GJ 3323, GJ
273, GJ 628 and GJ 3293, from which we derived radial velocities (RVs) and
spectroscopic activity indicators. We searched them for variabilities,
periodicities, Keplerian modulations and correlations, and attribute the
radial-velocity variations to combinations of planetary companions and stellar
activity. Results. We detect 12 planets, of which 9 are new with masses ranging
from 1.17 to 10.5 Mearth . Those planets have relatively short orbital periods
(P<40 d), except two of them with periods of 217.6 and 257.8 days. Among these
systems, GJ 273 harbor two planets with masses close to the one of the Earth.
With a distance of 3.8 parsec only, GJ 273 is the second nearest known
planetary system - after Proxima Centauri - with a planet orbiting the
circumstellar habitable zone.Comment: 19 pages, 24 figures. Astronomy and Astrophysics in pres
Multiple Molecular H2 Outflows in AFGL 618
We report high spatial (0.5 arcsec) and high spectral (9 km/s) resolution
spectro-imaging of the 2.12 micron H2 1-0 S(1) line in the proto-planetary
nebula AFGL 618 using BEAR at the CFHT. The observations reveal the presence of
multiple, high-velocity, molecular outflows that align with the remarkable
optical jets seen in HST images. The structure and kinematics of the outflows
show how jets interact with circumstellar gas and shape the environment in
which planetary nebulae form.Comment: 14 pages, 5 figures. To appear in The Astrophysical Journal Letter
The HARPS search for southern extra-solar planets XXXV. Planetary systems and stellar activity of the M dwarfs GJ 3293, GJ 3341, and GJ 3543
Context. Planetary companions of a fixed mass induce larger amplitude reflex
motions around lower-mass stars, which helps make M dwarfs excellent targets
for extra-solar planet searches. State of the art velocimeters with 1m/s
stability can detect very low-mass planets out to the habitable zone of these
stars. Low-mass, small, planets are abundant around M dwarfs, and most known
potentially habitable planets orbit one of these cool stars.
Aims. Our M-dwarf radial velocity monitoring with HARPS on the ESO 3.6m
telescope at La Silla observatory makes a major contribution to this sample.
Methods. We present here dense radial velocity (RV) time series for three M
dwarfs observed over years: GJ 3293 (0.42M), GJ 3341
(0.47M), and GJ 3543 (0.45M). We extract those RVs through
minimum matching of each spectrum against a high S/N ratio stack of
all observed spectra for the same star. We then vet potential orbital signals
against several stellar activity indicators, to disentangle the Keplerian
variations induced by planets from the spurious signals which result from
rotational modulation of stellar surface inhomogeneities and from activity
cycles.
Results. Two Neptune-mass planets - and
- orbit GJ 3293 with periods d and
d, possibly together with a super-Earth -
- with period . A super-Earth
- - orbits GJ 3341 with . The RV
variations of GJ 3543, on the other hand, reflect its stellar activity rather
than planetary signals.Comment: Accepted for publication in A&A, 19 pages, 12 figures, 7 table
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