Extremely broad radio recombination maser lines toward the high-velocity ionized jet in Cepheus A HW2

We present the first detection of the H40a, H34a and H31a radio recombination lines (RRLs) at millimeter wavelengths toward the high-velocity, ionized jet in the Cepheus A HW2 star forming region. From our single-dish and interferometric observations, we find that the measured RRLs show extremely broad asymmetric line profiles with zero-intensity linewidths of ~1100 kms-1. From the linewidths, we estimate a terminal velocity for the ionized gas in the jet of >500 kms-1, consistent with that obtained from the proper motions of the HW2 radio jet. The total integrated line-to-continuum flux ratios of the H40a, H34a and H31a lines are 43, 229 and 280 kms-1, clearly deviating from LTE predictions. These ratios are very similar to those observed for the RRL maser toward MWC349A, suggesting that the intensities of the RRLs toward HW2 are affected by maser emission. Our radiative transfer modeling of the RRLs shows that their asymmetric profiles could be explained by maser emission arising from a bi-conical radio jet with a semi-aperture angle of 18 deg, electron density distribution varying as r^(-2.11) and turbulent and expanding wind velocities of 60 and 500 kms-1.Comment: 6 pages, 2 figures, 3 tables, accepted for publication in ApJ

Expanded Very Large Array observations of the H66{\alpha} and He66{\alpha} recombination lines toward MWC 349A

We have used the greatly enhanced spectral capabilities of the Expanded Very Large Array to observe both the 22.3 GHz continuum emission and the H66{\alpha} recombination line toward the well-studied Galactic emission-line star MWC 349A. The continuum flux density is found to be 411 $\pm$ 41 mJy in good agreement with previous determinations. The H66{\alpha} line peak intensity is about 25 mJy, and the average line-to-continuum flux ratio is about 5%, as expected for local thermodynamic equilibrium conditions. This shows that the H66{\alpha} recombination line is not strongly masing as had previously been suggested, although a moderate maser contribution could be present. The He66{\alpha} recombination line is also detected in our observations; the relative strengths of the two recombination lines yield an ionized helium to ionized hydrogen abundance ratio y+ = 0.12 $\pm$ 0.02. The ionized helium appears to share the kinematics of the thermally excited ionized hydrogen gas, so the two species are likely to be well mixed. The electron temperature of the ionized gas in MWC 349A deduced from our observations is 6,300 $\pm$ 600 K.Comment: Accepted for publication in ApJ

Methanol detection in M82

We present a multilevel study of the emission of methanol, detected for the first time in this galaxy, and discuss the origin of its emission. The high observed methanol abundance of a few 10^-9 can only be explained if injection of methanol from dust grains is taken into account. While the overall [CH3OH]/[NH3] ratio is much larger than observed towards other starbursts, the dense high excitation component shows a similar value to that found in NGC 253 and Maffei 2. Our observations suggest the molecular material in M 82 to be formed by dense warm cores, shielded from the UV radiation and similar to the molecular clouds in other starbursts, surrounded by a less dense photodissociated halo. The dense warm cores are likely the location of recent and future star formation within M 82.Comment: Accepted for publication in A&A Letter

Coupling the dynamics and the molecular chemistry in the Galactic center

The physical conditions of the Galactic center (GC) clouds moving with non-circular velocities are not well-known. We have studied the physical conditions of these clouds with the aim of better understanding the origin of the outstanding physical conditions of the GC molecular gas and the possible effect of the large scale dynamics on these physical conditions.Using published CO(1-0) data, we have selected a set of clouds belonging to all the kinematical components seen in the longitude-velocity diagram of the GC. We have done a survey of dense gas in all the components using the J=2-1 lines of CS and SiO as tracers of high density gas and shock chemistry. We have detected CS and SiO emission in all the kinematical components. The gas density and the SiO abundance of the clouds in non-circular orbits are similar those in the nuclear ring (GCR). Therefore, in all the kinematical components there are dense clouds that can withstand the tidal shear. However, there is no evidence of star formation outside the GCR. The high relative velocity and shear expected in the dust-lanes along the bar major axis could inhibit the star formation process, as observed in other galaxies. The high SiO abundances derived in the non-circular velocity clouds are likely due to the large-scale shocks that created the dust lanesComment: One figure as an independent PDF file. Accepted by A&

A Molecular Counterpart to the Herbig-Haro 1-2 Flow

We present high angular resolution (12"-24") and high sensitivity 12CO and 13CO J=2-1 and J=1-0 observations of the HH 1-2 outflow. The observations show the molecular counterpart, moving with a velocity of approx. 30 km/s, of the optical bipolar system driven by the VLA 1 embedded source. Along the optical jet there are certain regions where the molecular gas reaches deprojected velocities of 100-200 km/s, and that we interpret as the molecular jet. The bipolar CO outflow has a length of approx. 260" with a curved morphology towards the North where it extends beyond the HH 1 object (approx. 120") . Two new molecular outflows have been detected, one arising from IRAS 05339-0647 which excites the HH 147 optical flow and another powered by VLA 2 which drives the HH 144 optical outflow. The molecular outflow driven by the VLA 3 source is also clearly detected and spatially resolved from the VLA 1 main outflow.Comment: 14 pages, 4 figures, accepted ApJLet

Fretting-Fatigue Analysis of Shot-Peened Al 7075-T651 Test Specimens

Shot peening is a mechanical treatment that induces several changes in the material: surface roughness, increased hardness close to the surface, and, the most important, compressive residual stresses. This paper analyzes the effect of this treatment on alloy Al 7075-T651 in the case of fretting fatigue with cylindrical contact through the results of 114 fretting fatigue tests. There are three independent loads applied in this type of test: a constant normal load N, pressing the contact pad against the specimen; a cyclic bulk stress σ in the specimen; and a cyclic tangential load Q through the contact. Four specimens at each of 23 different combinations of these three parameters were tested—two specimens without any treatment and two treated with shot peening. The fatigue lives, contact surface, fracture surface, and residual stresses and hardness were studied. Improvement in fatigue life ranged from 3 to 22, depending on fatigue life. The relaxation of residual-stress distribution related to the number of applied cycles was also measured. Finally, another group of specimens treated with shot peening was polished and tested, obtaining similar lives as in the tests with specimens that were shot-peened but not polished.Junta de Andalucía P12-TEP-263

Organic Molecules in the Galactic Center. Hot Core Chemistry without Hot Cores

We study the origin of large abundances of complex organic molecules in the Galactic center (GC). We carried out a systematic study of the complex organic molecules CH3OH, C2H5OH, (CH3)2O, HCOOCH3, HCOOH, CH3COOH, H2CO, and CS toward 40 GC molecular clouds. Using the LTE approximation, we derived the physical properties of GC molecular clouds and the abundances of the complex molecules.The CH3OH abundance between clouds varies by nearly two orders of magnitude from 2.4x10^{-8} to 1.1x10^{-6}. The abundance of the other complex organic molecules relative to that of CH3OH is basically independent of the CH3OH abundance, with variations of only a factor 4-8. The abundances of complex organic molecules in the GC are compared with those measured in hot cores and hot corinos, in which these complex molecules are also abundant. We find that both the abundance and the abundance ratios of the complex molecules relative to CH3OH in hot cores are similar to those found in the GC clouds. However, hot corinos show different abundance ratios than observed in hot cores and in GC clouds. The rather constant abundance of all the complex molecules relative to CH3OH suggests that all complex molecules are ejected from grain mantles by shocks. Frequent (similar 10^{5}years) shocks with velocities >6km/s are required to explain the high abundances in gas phase of complex organic molecules in the GC molecular clouds. The rather uniform abundance ratios in the GC clouds and in Galactic hot cores indicate a similar average composition of grain mantles in both kinds of regions. The Sickle and the Thermal Radio Arches, affected by UV radiation, show different relative abundances in the complex organic molecules due to the differentially photodissociation of these molecules.Comment: 18 pages, 10 Postscript figures, uses aa.cls, aa.bst, 10pt.rtx, natbib.sty, revsymb.sty revtex4.cls, aps.rtx and aalongtabl.sty. Accepted in A&A 2006. version 2. relocated figures and tables. Language editor suggestions. added reference

High-resolution study of a star-forming cluster in the Cep-A HW2 region

Due to its relatively small distance (725 pc), the Cepheus A East star-forming region is an ideal laboratory to study massive star formation processes. Based on its morphology, it has been suggested that the flattened molecular gas distribution around the YSO HW2 may be a 350-AU-radius massive protostellar disk. Goal of our work is to ascertain the nature of this structure. We have employed the Plateau de Bure Interferometer to acquire (sub-)arcsecond-resolution imaging of high-density and shock tracers, such as methyl cyanide (CH3CN) and silicon monoxide (SiO), towards the HW2 position. On the 1-arcsecond (about 725 AU) scale, the flattened distribution of molecular gas around HW2 appears to be due to the projected superposition, on the plane of the sky, of at least three protostellar objects, of which at least one is powering a molecular outflow at a small angle with respect to the line of sight. The presence of a protostellar disk around HW2 is not ruled out, but such structure is likely to be detected on a smaller spatial scale, or using different molecular tracers.Comment: 6 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

First detections of extragalactic SO2, NS and NO

We report the first detections of SO_2, NS and NO in an extragalactic source, the nucleus of the starburst galaxy NGC 253. Five SO_2 transitions, three groups of hyperfine components of NO and five of NS were detected. All three species show large abundances averaged over the inner 200 pc of NGC 253. With a relative abundance of a few 10^-7, the emission of the NO molecule is similar or even larger than that found in Galactic star forming regions. The derived relative molecular abundances for each molecule have been compared with those of prototypical Galactic molecular clouds. These results seem to confirm that large scale shocks dominate the chemistry of these molecules in the nucleus of NGC 253, ruling out a chemistry dominated by PDRs for the bulk of the gas.Comment: Accepted by A&A, 4 pages, 6 figure