arXiv subjects

Julieta P. Sanchez Arias

Publications and source records attributed to Julieta P. Sanchez Arias.

3 recordsLinked to original sources

arXiv2026

Characterization of the variability of the blue supergiant HD 14134

The post-main sequence (MS) evolution of massive stars encompasses phases in which the stars display high variability. One such class of objects are the blue supergiants which may be in either the pre- or post-red supergiant phase of their evolution. Their variability patterns might provide constraints for a proper classification of the objects. We aim to characterise the observed variability of the B supergiant HD14134 and to investigate the imprint of a time-variable wind on the brightness variation of the star and its impact on the detectability of pulsation signals. Spectroscopic data were collected over a 5-month period and combined with photometry from TESS. Stellar parameters were derived from modelling of the time-averaged spectrum with CMFGEN and the SED and were confirmed with stellar evolution models computed with MESA. The light curves and radial velocity curves of selected lines were analysed to determine pulsation signals. The wind variability and its imprint on the stellar brightness were investigated from an analysis of the Halpha line. Predictions of mode excitations were computed with the GYRE pulsation code and compared to the frequencies determined from the observations. A g-mode with a period of ~19.2 d and its harmonics are consistently detected in all data sets. The spectra unveil strong, non-periodic wind variability and 3 frequency signals were identified as due to this wind variability. The stellar parameters and age derived for HD14134 together with the absence of radial pulsations classify the star as a post-MS object evolving towards the red-supergiant stage, questioning its classification as alpha Cyg variable. The results reinforce that simultaneous long-term spectroscopic and photometric monitoring is indispensable for reliable frequency detections and for disentangling of variabilities imprinted by a time-variable wind from those imposed by pulsations.

astro-ph.SR↗

arXiv2021

Resolving the circumstellar environment of the Galactic B[e] supergiant star MWC 137. II. Nebular kinematics and stellar variability

The Galactic B[e] supergiant MWC 137 is surrounded by a large-scale optical nebula. To shed light on the physical conditions and kinematics of the nebula, we analyze the optical forbidden emission lines [NII] 6548,6583 and [SII] 6716,6731 in long-slit spectra taken with ALFOSC at the Nordic Optical Telescope. The radial velocities display a complex behavior but, in general, the northern nebular features are predominantly approaching while the southern ones are mostly receding. The electron density shows strong variations across the nebula with values spreading from about zero to ~800 cm$^{-3}$. Higher densities are found closer to MWC~137 and in regions of intense emission, whereas in regions with high radial velocities the density decreases significantly. We also observe the entire nebula in the two [SII] lines with the scanning Fabry-Perot interferometer attached to the 6-m telescope of the Special Astrophysical Observatory. These data reveal a new bow-shaped feature at PA = 225-245 and a distance 80" from MWC 137. A new H$α$ image has been taken with the Danish 1.54-m telescope on La Silla. No expansion or changes in the nebular morphology appear within 18.1 years. We derive a mass of 37 (+9/-5) solar masses and an age of $4.7\pm0.8$ Myr for MWC 137. Furthermore, we detect a period of 1.93 d in the time series photometry collected with the TESS satellite, which could suggest stellar pulsations. Other, low-frequency variability is seen as well. Whether these signals are caused by internal gravity waves in the early-type star or by variability in the wind and circumstellar matter currently cannot be distinguished.

astro-ph.SR↗

arXiv2018

Comparing the asteroseismic properties of pulsating pre-extremely low mass white dwarf and delta Scuti stars

Pulsating extremely low-mass pre-white dwarf stars (pre-ELMV), with masses between ~0.15 Msun and ~0.30 Msun, constitute a new class of variable stars showing g- and possibly p-mode pulsations with periods between 320 and 6000 s, while main sequence delta Scuti stars, with masses between 1.2-2.5 Msun, pulsate in low-order g and p modes with periods in the range [700-28800] s. Interestingly enough, the instability strips of pre-ELM white dwarf and delta Scuti stars nearly overlap in the Teff vs. log g diagram, leading to a degeneracy when spectroscopy is the only tool to classify the stars and pulsation periods only are considered. We employ adiabatic and non-adiabatic pulsation for models of pre-ELM and delta Scuti stars, and compare their pulsation periods, period spacings and rates of period change. We found substantial differences in the periods spacing of delta Scuti and pre-ELM white dwarf models. Even when the same period range is observed, the modes have distinctive signature in the period spacing and period difference values. For instance, the mean period difference of p- modes of consecutive radial orders for delta Scuti model are at least four times longer than the mean period spacing for the pre-ELM white dwarf model in the period range [2000 - 4600] s. In addition, the rate of period change is two orders of magnitudes larger for the pre-ELM white dwarfs compared to delta Scuti stars. In addition, we also report the discovery of a new variable star, SDSSJ075738.94+144827.50, located in the region of the Teff vs. log g diagram where these two kind of stars coexist. The characteristic spacing between modes of consecutive radial orders (p as well as g modes) and the large differences found in the rates of period change for delta Scuti and pre-ELM white dwarf stars suggest that asteroseismology can be employed to discriminate between these two groups of variable stars.

astro-ph.SR↗