3 research outputs found
YY Hya and its interstellar environment
No full textContext. During a search for previously unknown Galactic emission nebulae, we discovered a faint 36′ diameter Hα emission nebula centered around the periodic variable YY Hya. Although this star has been classified as an RR-Lyr variable, such a classification is inconsistent with a Gaia distance of ≃450 pc. The GALEX image data also show YY Hya as having a strong UV excess, suggesting the existence of a hot and compact binary companion.
Aims. We aim to clarify the nature of YY Hya and its nebula.
Methods. In addition to our discovery image data, we obtained a 2.°5 × 2.°5 image mosaic of the whole region with CHILESCOPE facilities and time-series spectroscopy at MDM observatory. Also, we used data from various space missions to derive an exact orbital period and a spectral energy distribution.
Results. We find that YY Hya is a compact binary system containing a K dwarf star that is strongly irradiated by a hot white dwarf companion. The spectral characteristics of the emission lines that are visible only during the maximum light of the perfectly sinusoidal optical light curve show signatures resembling those of members of the BE UMa variable family. These are post-common-envelope pre-cataclysmic variables. However, the companion star here is more massive than that found in other group members and, thus, the progenitor of the white dwarf must have been a star between 3 and 4 M⊙. The nebula appears to be an ejected common-envelope shell with a mass on the order of one M⊙ and an age of 500 000 yr. This makes it the biggest such shell known thus far. The alignment of neighboring nebulosities some 45′ to the northeast and southwest of YY Hya suggests that the system has had strong bipolar outflows. We also briefly speculate that it might be related to the 1065 BP “guest-star” reported in ancient Chinese records
The Spatial and Emission Properties of the Large [O III] Emission Nebula Near M31
No full textDrechsler et al. (2023) reported the unexpected discovery of a 1.5 degree
long [O III] emission nebula 1.2 degrees southeast of the M31 nucleus. Here we
present additional images of this large emission structure, called SDSO, along
with radial velocity and flux measurements from low-dispersion spectra.
Independent sets of [O III] images show SDSO to be composed of broad streaks of
diffuse emission aligned NE-SW. Deep H images reveal no strong
coincident emission suggesting a high [O III]/H ratio. We also find no
other [O III] emission nebulosity as bright as SDSO within several degrees of
M31 and no filamentary H emission connected to SDSO. Optical spectra
taken along the arc's northern limb reveal [O III] 4959,5007
emissions matching the location and extent seen in our [O III] images. The
heliocentric velocity of this [O III] nebulosity is km s
with a peak surface brightness of erg s
cm arcsec (0.55 Rayleigh). We discuss SDSO as a possible
unrecognized supernova remnant, a large and unusually nearby planetary nebula,
a stellar bow shock nebula, or an interaction of M31's outer halo gas with
high-velocity circumgalactic gas. We conclude that galactic origins for SDSO
are unlikely and favor instead an extragalactic M31 halo--circumgalactic cloud
interaction scenario, despite the nebula's low radial velocity. We then
describe new observations that may help resolve the nature and origin of this
large nebulosity so close to M31 in the sky.Comment: 20 pages, 13 figures, and 1 table; Revised and accepted for
publication in Ap
Deep Optical Emission-Line Images of Nine Known and Three New Galactic Supernova Remnants
No full textDeep optical emission-line images are presented for nine known plus three new
Galactic supernova remnants (SNRs), all but one having at least one angular
dimension greater than one degree. Wide-field images taken in H and [O
III] 5007 reveal many new and surprising remnant structures including
large remnant shock extensions and `breakout' features not seen in published
optical or radio data. These images represent over 12,000 individual images
totaling more than 1000 hours of exposure time taken over the last two years
mainly using small aperture telescopes which detected fainter nebular line
emissions than published emission-line images. During the course of this
imaging program, we discovered three new SNRs, namely G107.5-5.1 (the Nereides
Nebula), G209.9-8.2, and G210.5+1.3, two of which have diameters >1.5 degrees.
Besides offering greater structural detail on the nine already known SNRs, a
key finding of this study is the importance of [O III] emission-line imaging
for mapping the complete shock emissions of Galactic SNRs.Comment: 53 pages, 40 figures, 3 tables. Accepted for publication in the
Astrophysical Journal Supplement Serie
