701 research outputs found
The Radio Jet Associated with the Multiple V380 Ori System
The giant Herbig-Haro object 222 extends over 6 in the plane of the
sky, with a bow shock morphology. The identification of its exciting source has
remained uncertain over the years. A non-thermal radio source located at the
core of the shock structure was proposed to be the exciting source. However,
Very Large Array studies showed that the radio source has a clear morphology of
radio galaxy and a lack of flux variations or proper motions, favoring an
extragalactic origin. Recently, an optical-IR study proposed that this giant HH
object is driven by the multiple stellar system V380 Ori, located about 23
to the SE of HH 222. The exciting sources of HH systems are usually detected as
weak free-free emitters at centimeter wavelengths. Here we report the detection
of an elongated radio source associated with the Herbig Be star or with its
close infrared companion in the multiple V380 Ori system. This radio source has
the characteristics of a thermal radio jet and is aligned with the direction of
the giant outflow defined by HH~222 and its suggested counterpart to the SE,
HH~1041. We propose that this radio jet traces the origin of the large scale HH
outflow. Assuming that the jet arises from the Herbig Be star, the radio
luminosity is a few times smaller than the value expected from the
radio-bolometric correlation for radio jets, confirming that this is a more
evolved object than those used to establish the correlation.Comment: 13 pages, 3 figure
Near infrared and optical morphology of the dusty galaxy NGC972
Near infrared (NIR) and optical surface photometric analyses of the dusty
galaxy NGC972 are presented. The photometric profiles in the BVRJHK bands can
be fitted with a combination of gaussian and exponential profiles,
corresponding to a starburst nucleus and a stellar disk respectively. The
exponential scale length in the B-band is 2.8 times larger than in the K-band,
which implies a central B-band optical depth as high as 11. A bulge is absent
even in the NIR bands and hence the galaxy must be of a morphological type
later than the usually adopted Sb type. Relatively low rotational velocity and
high gas content also favor a later type, probably Sd, for the galaxy. Only one
arm can be traced in the distribution of old stars; the second arm, however,
can be traced in the distribution of dust and HII regions. Data suggest a short
NIR bar, which ends inside the nuclear ring. The slowly rising nature of the
rotation curve rules out a resonance origin of the the nuclear ring. The ring
is most likely not in the plane of the galaxy, given its circular appearance in
spite of the moderately high inclination of the galaxy. The off-planar nature
of the star forming ring, the unusually high fraction (30%) of the total mass
in molecular form, the presence of a nuclear starburst and the asymmetry of
spiral arms, are probably the result of a merger with a gas-rich companion
galaxy.Comment: Uses aas2pp4.sty and epsfig.sty, 12 pages To appear in Astronomical
Journal, October 199
Characterizing the dust content of disk substructures in TW Hya
We present Atacama Large Millimeter Array (ALMA) observations of TW Hya at
3.1 mm with milliarcsecond resolution. These new data were combined
with archival high angular resolution ALMA observations at 0.87 mm, 1.3 mm, and
2.1 mm. We analyze these multi-wavelength data to infer a disk radial profile
of the dust surface density, maximum particle size, and slope of the particle
size distribution. Most previously known annular substructures in the disk of
TW Hya are resolved at the four wavelengths. Inside the inner 3 au cavity, the
2.1 mm and 3.1 mm images show a compact source of free-free emission, likely
associated with an ionized jet. Our multi-wavelength analysis of the dust
emission shows that the maximum particle size in the disk of TW Hya is mm.
The inner 20 au are completely optically thick at all four bands, which results
in the data tracing different disk heights at different wavelengths. Coupled
with the effects of dust settling, this prevents the derivation of accurate
density and grain size estimates in these regions. At au, we find
evidence of the accumulation of large dust particle at the position of the
bright rings, indicating that these are working as dust traps. The total dust
mass in the disk is between 250 and 330 , which represents a
gas-to-dust mass ratio between 50 and 70. Our mass measurement is a factor of
4.5-5.9 higher than the mass that one would estimate using the typical
assumptions of large demographic surveys. Our results indicate that the ring
substructures in TW Hya are ideal locations to trigger the streaming
instability and form new generations of planetesimals.Comment: 22 pages, 17 figures, accepted for publication in A&A. Language
edited versio
Mechanical Identities of RNA and DNA Double Helices Unveiled at the Single-Molecule Level
[EN] Double-stranded (ds) RNA is the genetic material of a variety of viruses and has been recently recognized as a relevant molecule in cells for its regulatory role. Despite that the elastic response of dsDNA has been thoroughly characterized in recent years in single-molecule stretching experiments, an equivalent study with dsRNA is still lacking. Here, we have engineered long dsRNA molecules for their individual characterization contrasting information with dsDNA molecules of the same sequence. It is known that dsRNA is an A-form molecule unlike dsDNA, which exhibits B-form in physiological conditions. These structural types are distinguished at the single-molecule level with atomic force microscopy (AFM) and are the basis to understand their different elastic response. Force¿extension curves of dsRNA with optical and magnetic tweezers manifest two main regimes of elasticity, an entropic regime whose end is marked by the A-form contour- length and an intrinsic regime that ends in a low-cooperative overstretching transition in which the molecule extends to 1.7 times its A-form contour-length. DsRNA does not switch between the A and B conformations in the presence of force. Finally, dsRNA presents both a lower stretch modulus and overstretching transition force than dsDNA, whereas the electrostatic and intrinsic contributions to the persistence length are larger.This work was supported by grants from the Spanish Ministry of Science and Innovation (BFU2011-29038 and BFU2010-15703) and the Comunidad de Madrid (S2009/MAT/1507). IRA.-G. acknowledges a Ramon y Cajal contract from the Spanish Ministry of Science and Innovation (RYC-2007-01765). Work in the F.M.-H. laboratory was supported by a Starting Grant from the European Research Council (no. 206117) and a grant from the Spanish Ministry of Science and Innovation (FIS2011-24638). We thank M. S. Dillingham for kindly providing the pSP73-JY0 plasmid, M. Menendez for access to a spectropolarimeter, A. Monserrate for polylysine-AFM control experiments, and B. Ibarra for fruitful discussions.Herrero-Galán, E.; Fuentes-Perez. M.E.; Carrasco, C.; Valpuesta, J.; Carrascosa, J.; Moreno-Herrero, F.; Arias-Gonzalez, JR. (2013). Mechanical Identities of RNA and DNA Double Helices Unveiled at the Single-Molecule Level. Journal of the American Chemical Society. 135(1):122-131. https://doi.org/10.1021/ja3054755S122131135
Protostellar Outflows at the EarliesT Stages (POETS). II. A possible radio synchrotron jet associated with the EGO G035.02+0.35
Centimeter continuum observations of protostellar jets have revealed the
presence of knots of shocked gas where the flux density decreases with
frequency. This spectrum is characteristic of nonthermal synchrotron radiation
and implies the presence of both magnetic fields and relativistic electrons in
protostellar jets. Here, we report on one of the few detections of nonthermal
jet driven by a young massive star in the star-forming region G035.020.35.
We made use of the NSF's Karl G. Jansky Very Large Array (VLA) to observe this
region at C, Ku, and K bands with the A- and B-array configurations, and
obtained sensitive radio continuum maps down to a rms of 10 Jy
beam. These observations allow for a detailed spectral index analysis of
the radio continuum emission in the region, which we interpret as a
protostellar jet with a number of knots aligned with extended 4.5 m
emission. Two knots clearly emit nonthermal radiation and are found at similar
distances, of approximately 10,000 au, each side of the central young star,
from which they expand at velocities of hundreds km s. We estimate both
the mechanical force and the magnetic field associated with the radio jet, and
infer a lower limit of M yr km s and
values in the range mG, respectively.Comment: 10 pages, 4 figures, 5 tables, accepted by Astronomy & Astrophysic
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