arXiv subjects

Miriam García

Publications and source records attributed to Miriam García.

6 recordsLinked to original sources

arXiv2026

The future of high-resolution UV spectroscopy: Science with a UV Échelle spectrograph on the Habitable Worlds Observatory, or a dedicated mission

High-resolution UV spectroscopy serves a diversity of science cases, from small bodies to planets, stars, and galaxies, but is currently limited to the Hubble Space Telescope and bright targets. Major advances require increasing sensitivity by at least one order of magnitude. Here we present the UV science cases for PEGASUS (Planets, Earths, Galaxies, And Stars UV Spectrograph), a UV Échelle high-resolution spectrograph concept, with $R = λ/δλ\sim 100\,000$ (full range 10 000-140 000) and covering 90--400 nm, with a foreseen extension to at least 800 nm. PEGASUS is ideally suited for the Habitable Worlds Observatory (HWO), enabling transformative science across the UV/optical wavelength ranges. PEGASUS will be unique in high sensitivity (effective area) and high spectral resolution -- an uncharted territory -- as well as robustness, thanks to the simplicity of its design. Its UV science cases include: I) Formation and evolution of planets and their habitability: properties of exoplanets and atmospheres, protoplanetary disks, Solar System bodies; II) Stellar lives and deaths at their extremes: the first stars and the origin of the elements, compact and massive stars, Supernovae; III) Gas and metals in the baryon cycle of galaxies: the interstellar, circumgalactic, and intergalactic medium and their roles in galaxy growth. These are essential for the Astro Decadal 2020 Survey, Voyage 2050, and HWO. While this paper focuses on high-impact science enabled by UV high-resolution spectroscopy, PEGASUS will extend into the optical regime and lower spectral resolution, making it a multi-purpose, widely used, workhorse spectrograph for HWO.

astro-ph.IM↗

arXiv2022

The R136 star cluster dissected with Hubble Space Telescope/STIS. III. The most massive stars and their clumped winds

Context: The star cluster R136 inside the LMC hosts a rich population of massive stars, including the most massive stars known. The strong stellar winds of these very luminous stars impact their evolution and the surrounding environment. We currently lack detailed knowledge of the wind structure that is needed to quantify this impact. Aims: To observationally constrain the stellar and wind properties of the massive stars in R136, in particular the parameters related to wind clumping. Methods: We simultaneously analyse optical and UV spectroscopy of 53 O-type and 3 WNh-stars using the FASTWIND model atmosphere code and a genetic algorithm. The models account for optically thick clumps and effects related to porosity and velocity-porosity, as well as a non-void interclump medium. Results: We obtain stellar parameters, surface abundances, mass-loss rates, terminal velocities and clumping characteristics and compare these to theoretical predictions and evolutionary models. The clumping properties include the density of the interclump medium and the velocity-porosity of the wind. For the first time, these characteristics are systematically measured for a wide range of effective temperatures and luminosities. Conclusions: We confirm a cluster age of 1.0-2.5 Myr and derive an initial stellar mass of $\geq 250 {\rm M}_\odot$ for the most massive star in our sample, R136a1. The winds of our sample stars are highly clumped, with an average clumping factor of $f_{\rm cl}=29\pm15$. We find tentative trends in the wind-structure parameters as a function of mass-loss rate, suggesting that the winds of stars with higher mass-loss rates are less clumped. We compare several theoretical predictions to the observed mass-loss rates and terminal velocities and find that none satisfactorily reproduces both quantities. The prescription of Krtička & Kubát (2018) matches best the observed mass-loss rates.

astro-ph.SR↗

arXiv2019

Closing gaps to our origins. The UV window into the Universe

The investigation of the emergence of life is a major endeavour of science. Astronomy is contributing to it in three fundamental manners: (1) by measuring the chemical enrichment of the Universe, (2) by investigating planet formation and searching for exoplanets with signatures of life and, (3) by determining the abundance of aminoacids and the chemical routes to aminoacid and protein growth in astronomical bodies. This proposal deals with the first two. In the Voyage to 2050, the world-wide scientific community is getting equipped with large facilities for the investigation of the emergence of life in the Universe (i.e. VLT, JWST, ELT, GMT, TMT, ALMA, FAST, VLA, ATHENA, SKA) including the ESA's CHEOPS, PLATO and ARIEL missions. This white paper is a community effort to call for the development of a large ultraviolet optical observatory to gather fundamental data for this investigation that will not be accessible through other ranges of the electromagnetic spectrum. A versatile space observatory with UV sensitivity a factor of 50-100 greater than existing facilities will revolutionize our understanding of the pathway to life in the Universe.

astro-ph.SR↗

arXiv2018

Identifying two groups of massive stars aligned in the $l\sim38^{\circ}$ Galactic direction

Context: Recent near-infrared data have contributed to unveil massive and obscured stellar populations in both new and previously known clusters in our Galaxy. These discoveries lead us to view the Milky Way as an active star-forming machine. Aims: We look for young massive cluster candidates as over-densities of OB-type stars. The first search, focused on the Galactic direction $l=38^{\circ}$, resulted in the detection of two objects with a remarkable population of OB-type star candidates. Methods: With a modified version of the friends-of-friends algorithm AUTOPOP and using 2MASS and UKIDSS-GPS near-infrared ($J$, $H$, and $K$) photometry for one of our cluster candidates (named Masgomas-6) we selected 30 stars for multi-object and long-slit $H$- and $K$-spectroscopy. With the spectral classification and the near-infrared photometric data, we derive individual distance, extinction and radial velocity. Results: Of the 30 spectroscopically observed stars, 20 are classified as massive stars, including OB-types (dwarfs, giants and supergiants), two red supergiants, two Wolf-Rayet (WR122-11 and the new WR122-16), and one transitional object (the LBV candidate IRAS 18576+0341). The individual distances and radial velocities do not agree with a single cluster, indicating that we are observing two populations of massive stars in the same line-of-sight: Masgomas-6a and Masgomas-6b. The first group of massive stars, located at 3.9$^{+0.4}_{-0.3}$ kpc, contains both Wolf-Rayets and most of the OB-dwarfs, and Masgomas-6b, at $9.6\pm0.4$ kpc, hosts the LBV candidate and an evolved population of supergiants. We are able to identify massive stars at two Galactic arms, but we can not clearly identify whether these massive stars form clusters or associations.

astro-ph.SR↗

arXiv2013

Building galaxies, stars, planets and the ingredients for life between the stars. A scientific proposal for a European Ultraviolet-Visible Observatory (EUVO)

The growth of luminous structures and the building blocks of life in the Universe began as primordial gas was processed in stars and mixed at galactic scales. The mechanisms responsible for this development are not well understood and have changed over the intervening 13 billion years. To follow the evolution of matter over cosmic time, it is necessary to study the strongest (resonance) transitions of the most abundant species in the Universe. Most of them are in the ultraviolet (UV; 950A-3000A) spectral range that is unobservable from the ground. A versatile space observatory with UV sensitivity a factor of 50-100 greater than existing facilities will revolutionize our understanding of the Universe. Habitable planets grow in protostellar discs under ultraviolet irradiation, a by-product of the star-disk interaction that drives the physical and chemical evolution of discs and young planetary systems. The electronic transitions of the most abundant molecules are pumped by the UV field, providing unique diagnostics of the planet-forming environment that cannot be accessed from the ground. Earth's atmosphere is in constant interaction with the interplanetary medium and the solar UV radiation field. A 50-100 times improvement in sensitivity would enable the observation of the key atmospheric ingredients of Earth-like exoplanets (carbon, oxygen, ozone), provide crucial input for models of biologically active worlds outside the solar system, and provide the phenomenological baseline to understand the Earth atmosphere in context. In this white paper, we outline the key science that such a facility would make possible and outline the instrumentation to be implemented.

astro-ph.IM↗

arXiv2012

Massive Stars: Key to Solving the Cosmic Puzzle

We describe observations in the nearby universe (<100 Mpc) with a 10-m or larger space-based telescope having imaging and spectral capabilities in the range 912-9000 Åthat would enable advances in the fields of massive stars, young populations, and star-forming galaxies, that are essential for achieving the Cosmic Origins Program objectives i) how are the chemical elements distributed in galaxies and dispersed in the circumgalactic and intergalactic medium; and ii) when did the first stars in the universe form, and how did they influence their environments. We stress the importance of observing hundreds of massive stars and their descendants individually, which will make it possible to separate the many competing factors that influence the observed properties of these systems (mass, composition, convection, mass-loss, rotation rate, binarity, magnetic fields, and cluster mass).

astro-ph.SR↗