arXiv subjects

S. Pacheco-Vázquez

Publications and source records attributed to S. Pacheco-Vázquez.

3 recordsLinked to original sources

arXiv2018

Re-visiting the case of R Mon: Is CO removed at R<20 au?

To our knowledge, R Mon is the only B0 star in which a gaseous Keplerian disk has been detected. However, there is some controversy about the spectral type of R Mon. Some authors propose that it could be a later B8e star, where disks are more common. We have re-evaluated the spectral type of R Mon using the available continuum data and UVES emission lines. We used a power-law disk model to fit previous 12 CO 1-0 and 2-1 interferometric observations and the PACS CO data to investigate the disk structure. Interferometric detections of 13 CO J=1-0, HCO+ 1-0, and CN 1-0 lines using the IRAM Plateau de Bure Interferometer (PdBI) are presented. The HCN 1-0 line was not detected. Our analysis confirms that R Mon is a B0 star. The disk model compatible with the 12 CO 1-0 and 2-1 interferometric observations falls short of predicting the observed fluxes of the 14 31 CO lines suggest the existence of a region empty of CO at R<20 au in the proto-planetary disk. The intense emission of the HCO+ and CN lines shows the strong influence of UV photons on gas chemistry. The observations gathered in this paper are consistent with the presence around R Mon of a transition disk with a cavity about 20 au. This size is similar to the photoevaporation radius that supports the interpretation that UV photoevaporation is main disk dispersal mechanism in massive stars

astro-ph.SR↗

arXiv2016

High spatial resolution imaging of SO and H2CO in AB Auriga: the first SO image in a transitional disk

Transitional disks are structures of dust and gas around young stars with large inner cavities in which planet formation may occur. Lopsided dust distributions are observed in the dust continuum emission at millimeter wavelengths. These asymmetrical structures can be explained as the result of an enhanced gas density vortex where the dust is trapped potentially promoting the rapid growth to the planetesimal scale. AB Aur hosts a transitional disk with a clear horseshoe morphology which strongly suggests the presence of a dust trap. Our goal is to investigate its formation and the possible effects on the gas chemistry. We used the NOEMA interferometer to image the 1mm continuum dust emission and the 13CO J=2->1, C18O J=2->1, SO J=56->45 and H2CO J=303->202 rotational lines. Line integrated intensity ratio images are built to investigate the chemical changes within the disk. We have used a single point (n,T) chemical model to investigate the lifetime of gaseous CO, H2CO and SO in the dust trap. Our model shows that for densities >10^7 cm^-3, the SO molecules are depleted (directly frozen or converted into SO2 and then frozen out) in less than 0.1 Myr. The lower SO abundance towards the dust trap could indicate that a larger fraction of the gas is in a high density environment. Gas dynamics, grain growth and gas chemistry are coupled in the planet formation process. Because of the strong dependence of SO abundance on the gas density, the sulfur chemistry can be used as a chemical diagnostic to detect the birthsites of future planets. However, the large uncertainties inherent to chemical models and the limited knowledge of the disk physical structure and initial conditions are important drawbacks.

astro-ph.SR↗

arXiv2015

Chemical composition of the circumstellar disk around AB Aurigae

Aims. Our goal is to determine the molecular composition of the circumstellar disk around AB Aurigae (hereafter, AB Aur). AB Aur is a prototypical Herbig Ae star and the understanding of its disk chemistry is of paramount importance to understand the chemical evolution of the gas in warm disks. Methods. We used the IRAM 30-m telescope to perform a sensitive search for molecular lines in AB Aur as part of the IRAM Large program ASAI (A Chemical Survey of Sun-like Star-forming Regions). These data were complemented with interferometric observations of the HCO+ 1-0 and C17O 1-0 lines using the IRAM Plateau de Bure Interferometer (PdBI). Single-dish and interferometric data were used to constrain chemical models. Results. Throughout the survey, several lines of CO and its isotopologues, HCO+, H2CO, HCN, CN and CS, were detected. In addition, we detected the SO 54-33 and 56-45 lines, confirming the previous tentative detection. Comparing to other T Tauri's and Herbig Ae disks, AB Aur presents low HCN 3-2/HCO+ 3-2 and CN 2-1/HCN 3-2 line intensity ratios, similar to other transition disks. AB Aur is the only protoplanetary disk detected in SO thus far. Conclusions. We modeled the line profiles using a chemical model and a radiative transfer 3D code. Our model assumes a flared disk in hydrostatic equilibrium. The best agreement with observations was obtained for a disk with a mass of 0.01 Msun , Rin=110 AU, Rout=550 AU, a surface density radial index of 1.5 and an inclination of 27 deg. The intensities and line profiles were reproduced within a factor of 2 for most lines. This agreement is reasonable taking into account the simplicity of our model that neglects any structure within the disk. However, the HCN 3-2 and CN 2-1 line intensities were predicted more intense by a factor of >10. We discuss several scenarios to explain this discrepancy.

astro-ph.EP↗