arXiv subjects

V. M. A. Gomez-Gonzalez

Publications and source records attributed to V. M. A. Gomez-Gonzalez.

4 recordsLinked to original sources

arXiv2023

X-Shooting ULLYSES: massive stars at low metallicity. I. Project Description

Observations of individual massive stars, super-luminous supernovae, gamma-ray bursts, and gravitational-wave events involving spectacular black-hole mergers, indicate that the low-metallicity Universe is fundamentally different from our own Galaxy. Many transient phenomena will remain enigmatic until we achieve a firm understanding of the physics and evolution of massive stars at low metallicity (Z). The Hubble Space Telescope has devoted 500 orbits to observe 250 massive stars at low Z in the ultraviolet (UV) with the COS and STIS spectrographs under the ULLYSES program. The complementary ``X-Shooting ULLYSES'' (XShootU) project provides enhanced legacy value with high-quality optical and near-infrared spectra obtained with the wide-wavelength coverage X-shooter spectrograph at ESO's Very Large Telescope. We present an overview of the XShootU project, showing that combining ULLYSES UV and XShootU optical spectra is critical for the uniform determination of stellar parameters such as effective temperature, surface gravity, luminosity, and abundances, as well as wind properties such as mass-loss rates in function of Z. As uncertainties in stellar and wind parameters percolate into many adjacent areas of Astrophysics, the data and modelling of the XShootU project is expected to be a game-changer for our physical understanding of massive stars at low Z. To be able to confidently interpret James Webb Space Telescope (JWST) spectra of the first stellar generations, the individual spectra of low Z stars need to be understood, which is exactly where XShootU can deliver.

astro-ph.SR↗

arXiv2021

Tomography of the unique on-going jet in the planetary nebula NGC 2392

Jets (fast collimated outflows) are claimed to be the main shaping agent of the most asymmetric planetary nebula (PNe) as they impinge on the circumstellar material at late stages of the asymptotic giant branch (AGB) phase. The first jet detected in a PN was that of NGC 2392, yet there is no available image because its low surface brightness contrast with the bright nebular emission. Here we take advantage from the tomographic capabilities of GTC MEGARA high-dispersion integral field spectroscopic observations of the jet in NGC 2392 to gain unprecedented details of its morphology and kinematics. The jet of NGC 2392 is found to emanate from the central star, break through the walls of the inner shell of this iconic PN and extend outside the nebula's outermost regions with an S-shaped morphology suggestive of precession. At odds with the fossil jets found in mature PNe, the jet in NGC 2392 is currently being collimated and launched. The high nebular excitation of NGC 2392, which implies a He$^{++}$/He ionization fraction too high to be attributed to the known effective temperature of the star, has been proposed in the past to hint at the presence of a hot white dwarf companion. In conjunction with the hard X-ray emission from the central star, the present-day jet collimation would support the presence of such a double-degenerate system where one component undergoes accretion from a remnant circumbinary disk of the common envelope phase.

astro-ph.SR↗

arXiv2020

MEGARA-IFU detection of extended HeII4686 nebular emission in the central region of NGC1569 and its ionization budget

We here report the detection of extended HeII4686 nebular emission in the central region of NGC1569 using the integral field spectrograph MEGARA at the 10.4-m Gran Telescopio Canarias. The observations cover a Field of View (FoV) of 12.5 arcsec x 11.3 arcsec at seeing-limited spatial resolution of ~15 pc and at a spectral resolution of R=6000 in the wavelength range 4330--5200 Angstrom. The emission extends over a semi-circular arc of ~40 pc width and ~150 pc diameter around the super star cluster A (SSC-A). The Av derived using Balmer decrement varies from the Galactic value of 1.6 mag to a maximum of ~4.5 mag, with a mean value of 2.65+/-0.60 mag. We infer 124+/-11 Wolf-Rayet (WR) stars in SSC-A using the HeII4686 broad feature and Av=2.3 mag. The He+ ionizing photon rate from these WR stars is sufficient to explain the luminosity of the HeII4686 nebula. The observationally-determined total He+ and H0 ionizing photon rates, their ratio, and the observed number of WR stars in SSC-A are all consistent with the predictions of simple stellar population models at an age of 4.0+/-0.5 Myr, and mass of (5.5+/-0.5)x10^5 Msun. Our observations reinforce the absence of WR stars in SSC-B, the second most massive cluster in the FoV. None of the other locations in our FoV where HeII4686 emission has been reported from narrow-band imaging observations contain WR stars.

astro-ph.GA↗

arXiv2016

Wolf-Rayet stars in M81: Detection and Characterization using GTC/OSIRIS spectra and HST/ACS images

We here report the properties of Wolf-Rayet (W-R) stars in 14 locations in the nearby spiral galaxy M81. These locations were found serendipitously while analysing the slit spectra of a sample of ~150 star-forming complexes, taken using the long-slit and Multi-Object spectroscopic modes of the OSIRIS instrument at the 10.4-m Gran Telescopio Canarias. Colours and magnitudes of the identified point sources in the Hubble Space Telescope images compare well with those of individual W-R stars in the Milky Way. Using templates of individual W-R stars, we infer that the objects responsible for the observed W-R features are single stars in 12 locations, comprising of 3 WNLs, 3 WNEs, 2 WCEs and 4 transitional WN/C types. In diagrams involving bump luminosities and the width of the bumps, the W-R stars of the same sub-class group together, with the transitional stars occupying locations intermediate between the WNE and WCE groups, as expected from the evolutionary models. However, the observed number of 4 transitional stars out of our sample of 14 is statistically high as compared to the 4% expected in stellar evolutionary models.

astro-ph.GA↗