Mapping the circumstellar SiO maser emission in R Leo

The study of the innermost circumstellar layers around AGB stars is crucial to understand how these envelopes are formed and evolve. The SiO maser emission occurs at a few stellar radii from the central star, providing direct information on the stellar pulsation and on the chemical and physical properties of these regions. Our data also shed light on several aspects of the SiO maser pumping theory that are not well understood yet. We aim to determine} the relative spatial distribution of the 43 GHz and 86 GHz SiO maser lines in the oxygen-rich evolved star R Leo. We have imaged with milliarcsecond resolution, by means of Very Long Baseline Interferometry, the 43 GHz (28SiO v=1, 2 J=1-0 and 29SiO v=0 J=1-0) and 86 GHz (28SiO v=1 J=2-1 and 29SiO v=0 J=2-1) masing regions. We confirm previous results obtained in other oxygen-rich envelopes. In particular, when comparing the 43 GHz emitting regions, the 28SiO v=2 transition is produced in an inner layer, closer to the central star. On the other hand, the 86 GHz line arises in a clearly farther shell. We have also mapped for the first time the 29SiO v=0 J=1-0 emission in R Leo. The already reported discrepancy between the observed distributions of the different maser lines and the theoretical predictions is also found in R Leo.Comment: accepted for publication in A&

The molecular envelope of CRL 618: A new model based on Herschel/HIFI observations

We study the physical properties and molecular excitation of the different warm gas components found in the protoplanetary nebula CRL 618. We revise our previous Herschel/HIFI observations, which consist of several 12CO and 13CO lines in the far-infrared/sub-mm band. These data have been re-analyzed in detail by improving calibration, the signal-to-noise-ratio, and baseline substraction. We identify the contributions of the different nebular components to the line profiles. We have used a spatio-kinematical model to better constrain the temperature, density, and kinematics of the molecular components probed by the improved CO observations. The 12CO and 13CO J=16-15, J=10-9, and J=6-5 transitions are detected in this source. The line profiles present a composite structure showing spectacular wings in some cases, which become dominant as the energy level increases. Our analysis of the high-energy CO emission with the already known low-energy J=2-1 and J=1-0 lines confirms that the high-velocity component, or fast bipolar outflow, is hotter than previously estimated with a typical temperature of ~300 K. This component may then be an example of a very recent acceleration of the gas by shocks that has not yet cooled down. We also find that the dense central core is characterized by a very low expansion velocity, ~5 km/s, and a strong velocity gradient. We conclude that this component is very likely to be the unaltered circumstellar layers that are lost in the last AGB phase, where the ejection velocity is particularly low. The physical properties of the other two nebular components, the diffuse halo and the double empty shell, more or less agrees with the estimations derived in previous models.Comment: Accepted for publication in Astronomy & Astrophysics. 8 pages, 3 figure

Preliminary results on SiO v=3 J=1-0 maser emission from AGB stars

We present the results of SiO maser observations at 43GHz toward two AGB stars using the VLBA. Our preliminary results on the relative positions of the different J=1-0 SiO masers (v=1,2 and 3) indicate that the current ideas on SiO maser pumping could be wrong at some fundamental level. A deep revision of the SiO pumping models could be necessary.Comment: poster, 2 pages, 2 figures, Proc. IAU Symp. 287 "Cosmic Masers: from OH to H0", R.S. Booth, E.M.L. Humphreys and W.H.T. Vlemmings, ed

SiO masers from AGB stars in the vibrationally excited v=1,v=2, and v=3 states

The v=1 and v=2 J=1-0 (43 GHz), and v=1 J=2-1 (86 GHz) SiO masers are intense in AGB stars and have been mapped using VLBI showing ring-like distributions. Those of the v=1, v=2 J=1-0 masers are similar, but the spots are rarely coincident, while the v=1 J=2-1 maser arises from a well separated region farther out. These relative locations can be explained by models tools that include the overlap of two IR lines of SiO and H2O. The v=3 J=1-0 line is not directly affected by any line overlap and its spot structure and position, relative to the other lines, is a good test to the standard pumping models. We present single-dish and simultaneous VLBI observations of the v=1, v=2, and v=3 J=1-0 maser transitions of 28SiO in several AGB stars. The spatial distribution of the SiO maser emission in the v=3 J=1-0 transition from AGB stars is systematically composed of a series of spots that occupy a ring-like structure. The overall ring structure is extremely similar to that found in the other 43 GHz transitions and is very different from the structure of the v=1 J=2-1 maser. The positions of the individual spots of the different 43 GHz lines are, however, very rarely coincident, which in general is separated by about 0.3 AU (between 1 and 5 mas). These results are very difficult to reconcile with standard pumping models, which predict that the masers of rotational transitions within a given vibrational state require very similar excitation conditions, while the transitions of different vibrational states should appear in different positions. However, models including line overlap tend to predict v=1, v=2, v=3 J=1-0 population inversion to occur under very similar conditions, while the requirements for v=1 J=2-1 appear clearly different, and are compatible with the observational results.Comment: 9 pages, 4 figures accepted by A&

O-GlcNAcylation enhances CPS1 catalytic efficiency for ammonia and promotes ureagenesis

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAMLife-threatening hyperammonemia occurs in both inherited and acquired liver diseases affecting ureagenesis, the main pathway for detoxification of neurotoxic ammonia in mammals. Protein O-GlcNAcylation is a reversible and nutrient-sensitive post-translational modification using as substrate UDP-GlcNAc, the end-product of hexosamine biosynthesis pathway. Here we show that increased liver UDP-GlcNAc during hyperammonemia increases protein O-GlcNAcylation and enhances ureagenesis. Mechanistically, O-GlcNAcylation on specific threonine residues increased the catalytic efficiency for ammonia of carbamoyl phosphate synthetase 1 (CPS1), the rate-limiting enzyme in ureagenesis. Pharmacological inhibition of O-GlcNAcase, the enzyme removing O-GlcNAc from proteins, resulted in clinically relevant reductions of systemic ammonia in both genetic (hypomorphic mouse model of propionic acidemia) and acquired (thioacetamide-induced acute liver failure) mouse models of liver diseases. In conclusion, by fine-tuned control of ammonia entry into ureagenesis, hepatic O-GlcNAcylation of CPS1 increases ammonia detoxification and is a novel target for therapy of hyperammonemia in both genetic and acquired diseasesThis work was supported by grants of Fondazione Telethon Italy (to N.B.‐P.), MIUR (PRIN2017 to N.B.‐P.), of the Swiss National Science Foundation (grant 320030_176088 to J.H.), of the US National Institutes of Health grants (R21NS091654 and R01NS100979 both to G.S.L.), of the Spanish Ministry of Science and Innovation (PID2019-105344RB-I00/AEI/10.13039/501100011033 toL.R.D. and E.R.), and by a Wellcome Trust Investigator Award (110061to D.M.F.v.A.

First VLBI mapping of circumstellar 29SiO maser emission

We report the first VLBI map of the v=0 J=1-0 maser line of 29SiO in the long-period variable star IRC+10011. We have found that this maser emission is composed of multiple spots distributed in an incomplete ring, suggesting that this maser is also amplified tangentially, as already proposed in other SiO circumstellar masers. We present also VLBI maps for the 7 mm 28SiO v=1 and 2 J=1-0 and the 3 mm v=1 J=2-1 lines. The 29SiO masing region appears to be located in a layer in between the 28SiO v=1 J=1-0 and 28SiO v=1 J=2-1 lines. In addition, we confirm that the 86 GHz maser v=1 J=2-1 forms in an outer region of the circumstellar envelope compared to the other 28SiO masers studied. Finally, we discuss the possible implications of the observational results on the SiO maser pumping theory.Comment: 4 pages, 2 figures. Accepted for publication in A&A Letter