arXiv subjects

Gladis Magris

Publications and source records attributed to Gladis Magris.

5 recordsLinked to original sources

arXiv2026

Understanding Balmer Decrements in T Tauri stars in terms of Multiflow Magnetospheric Accretion

Magnetospheric accretion is the paradigm for accretion in Classical T-Tauri Stars (CTTS). However, the standard, one-flow magnetospheric accretion model fails to replicate important characteristics such as the observed Balmer decrements. We address this limitation by adopting a model with two axisymmetric magnetospheric accretion flows of different accretion rates and geometries. We calculate the fluxes of the hydrogen $H_\alpha$, $H_\beta$, and $H_\gamma$ lines of each flow with the magnetospheric accretion model and use Bayesian statistics to fit the Balmer line fluxes of 139 CTTS in the Orion OB1b subassociation, and in the Upper Scorpius, Lupus and Chamaeleon I star-forming regions. We find that the Balmer decrements and line fluxes can be fitted by two distinct but coexisting flows: a compact, high accretion rate flow, close to the star and narrow (mean inner radius $R_i \sim 2.9 R_*$ and mean width $\Delta R \sim 0.7 R_*$), covering a few percent of the emitting area, and a more spread out flow, thicker ($\Delta R \sim 1.2 R_*$), and larger ($R_i \sim 3.7 R_*$), with lower accretion rate, encompassing the rest of the emitting area. The two-flow model can also reproduce the empirical correlation between the luminosity in $H_\alpha$ and the accretion luminosity. Overall, our findings suggest that a multicolumn approach provides a more accurate representation of the observed Balmer line emission, in agreement with results of numerical simulations.

astro-ph.SR↗

arXiv2024

RR Lyrae Stars in Intermediate-age Magellanic Clusters: Membership Probabilities and Delay Time Distribution

Recent works have challenged our canonical view of RR Lyrae (RRL) stars as tracers of exclusively old populations ($\gtrsim10$~Gyr) by proposing a fraction of these stars to be of intermediate ages ($\sim$2-5~Gyr). Since it is currently not possible to infer stellar ages directly for individual RRL stars, our goal in this work is to search for these in association to intermediate-age clusters whose reliable ages can then be safely be attributed to the RRL. We used the Gaia DR3 Specific Object Study and OGLE IV public catalogues to search for RRL stars around stellar clusters older than 1~Gyr in the Large and Small Magellanic Clouds. Modelling membership probabilities based on proper motion and photometric distance we obtained a list of 259 RRL stars associated with Magellanic clusters. Of these, 23 RRL are likely members of 10 intermediate-age clusters: 3 and 7 in the Small and Large Magellanic Clouds, respectively. By modelling the inferred expectation values of the number of RRL stars per cluster, we inferred the delay time distribution of the RRL in three age ranges. For the old population ($>8$~Gyr) we find $2.5^{+0.4}_{-0.3}$ RRL$/10^5 M_\odot$. For the young (1-2 Gyr) and intermediate age (2-8 Gyr) populations we find rates of $0.34^{+0.17}_{-0.12}$ and $0.071^{+0.073}_{-0.041}$ RRL$/10^5 M_\odot$, respectively, after further decontamination from control field tests. While radial velocities are necessary for definitively confirming cluster memberships, the high-probability list of intermediate-age RRL stars presented here offers a promising opportunity for the first direct confirmation of these enigmatic stars.

astro-ph.GA↗

arXiv2023

Constraints on star formation in Orion A from Gaia

We develop statistical methods within a Bayesian framework to infer the star formation history from photometric surveys of pre-main sequence populations. Our procedures include correcting for biases due to extinction in magnitude-limited surveys, and using distributions from subsets of stars with individual extinction measurements. We also make modest corrections for unresolved binaries. We apply our methods to samples of populations with Gaia photometry in the Orion A molecular cloud. Using two well-established sets of evolutionary tracks, we find that, although our sample is incomplete at youngest ages due to extinction, star formation has proceeded in Orion A at a relatively constant rate between ages of about 0.3 and 5 Myr, in contrast to other studies suggesting multiple epochs of star formation. Similar results are obtained for a set of tracks that attempt to take the effects of strong magnetic fields into account. We also find no evidence for a well-constrained "birthline" that would result from low-mass stars appearing first along the deuterium-burning main sequence, especially using the magnetic evolutionary tracks. While our methods have been developed to deal with Gaia data, they may be useful for analyzing other photometric surveys of star-forming regions.

astro-ph.SR↗

arXiv2014

Leaving the dark ages with AMIGA

We present an Analytic Model of Intergalactic-medium and GAlaxy evolution since the dark ages. AMIGA is in the spirit of the popular semi-analytic models of galaxy formation, although it does not use halo merger trees but interpolates halo properties in grids that are progressively built. This strategy is less memory-demanding and allows one to start the modeling at redshifts high enough and halo masses low enough to have trivial boundary conditions. The number of free parameters is minimized by making the causal connection between physical processes usually treated as independent from each other, which leads to more reliable predictions. But the strongest points of AMIGA are: i) the inclusion of molecular cooling and metal-poor, population III (Pop III) stars, with the most dramatic feedback, and ii) the accurate follow-up of the temperature and volume filling factor of neutral, singly, and doubly ionized regions, taking into account the distinct halo mass functions in those environments. We find the following general results. Massive Pop III stars determine the IGM metallicity and temperature, and the growth of spheroids and disks is self-regulated by that of massive black holes developed from the remnants of those stars. Yet, the properties of normal galaxies and active galactic nuclei appear to be quite insensitive to Pop III star properties owing to the much higher yield of ordinary stars compared to Pop III stars and the dramatic growth of MBHs when normal galaxies begin to develop, which cause the memory loss of the initial conditions.

astro-ph.GA↗

arXiv1997

A Revised Age for the z=1.55 Galaxy LBDS 53W091

Empirical evidence suggests that the stellar population in LBDS 53W091 is significantly younger than that in M32. Population synthesis models indicate that the age of LBDS 53W091 is in the range from 1 to 2 Gyr and depends on the specific model. Older ages require sub-solar metallicity models. The estimates of the age of the dominant population in M32 range from 3 to 5 Gyr and depend not only on the model but also on the SED of this galaxy used in the fits. The same models predict an age of 11 to 13 Gyr for the stars in a typical old E/S0 galaxy. A 1 to 2 Gyr old galaxy at z = 1.55 poses no problem for the Lambda = 0, Omega = 1 universe, as long as h <= 0.8. The most likely reason for the difference between our age estimate and the value of 3.5 Gyr derived by Dunlop et al. (1996), is the fact that these authors did not require that the population synthesis models that they used fitted simultaneously the UV break amplitudes and the observed $R-J, R-H$, and $R-K$ colors of this galaxy. As we will discuss elsewhere, a comparison of our results with those by Spinrad et al. (1997) shows that our conclusions still hold. The paper by Spinrad et al. was unknown to us at the time of this Conference.

astro-ph↗