Searcharxiv⌕ Search

arXiv subjects

Iman Behbehani

Publications and source records attributed to Iman Behbehani.

2 recordsLinked to original sources

Searching for Dwarf Novae in 47 Tucanae

The globular cluster 47 Tucanae has 43 strong cataclysmic variable candidates, four of which are confirmed dwarf novae. Tidal capture theory predicts the existence of dozens of dwarf novae, suggesting more are undiscovered. Using 435 nm and 475 nm long exposure images from Hubble's ACS camera, we searched five epochs of archival Hubble images and did not find any variability at the scale of a dwarf nova eruption. We found 1 previously undiscovered variable object on the main sequence that could not be classified as a CV; the object experienced a change of approximately 0.3 Mag in 425 nm, and 0.2 mag in 635 nm over the course of 12 days. The lack of new CV detections in 47 Tucanae could be a result of the short timescale of the DN eruption, and a low observing probability. However, this null result may also support research suggesting most CVs in globular clusters are not dynamically formed, and tidal capture theory overestimates the detectable CV population.

astro-ph.SR↗

Betelgeuse, Betelgeuse, Betelgeuse, Betel-buddy? Constraints on the dynamical companion to $α$ Orionis from HST

Recently, two independent analyses have asserted that the cause of the Long Secondary Period (LSP) observed in the variability spectrum of our nearest red supergiant, Betelgeuse ($α$ Ori), is an as-yet undetected, low-mass binary companion dubbed $α$ Ori B. In this paper, we present the results of a far-UV observational campaign using the STIS echelle spectrograph on the Hubble Space Telescope aimed at detecting spectral signatures of the companion. The four-quadrant tiling pattern and timing of the observations were optimized to isolate the companion, with observations taking place during a period of maximum angular and velocity separation between Betelgeuse and the putative companion. Spectral differencing between quadrants recovers no spectral features at the companion's velocity in excess of the background or Betelgeuse's chromosphere, i.e. a non-detection. Having determined that $α$ Ori B is most likely a Young Stellar Object (YSO) thanks to constraints from a complementary X-ray campaign with the Chandra X-ray Observatory in a companion paper, comparison of our data against canonical spectra from YSOs in the ULLYSES database allows us to confidently exclude masses above $\gtrsim1.5M_\odot$ and companion continuum or line emission in excess of $\approx10^{-14}$ erg s$^{-1}$ cm$^{-2}$ angstrom$^{-1}$ in the FUV ($\approx1200-1700$ angstroms). Future observational campaigns aware of the LSP phase are needed to place deeper constraints on the spectroscopic nature of $α$ Ori B.

astro-ph.SR↗