1,359 research outputs found
The planetary nebula IC 4776 and its post-common-envelope binary central star
We present a detailed analysis of IC 4776, a planetary nebula displaying a
morphology believed to be typical of central star binarity. The nebula is shown
to comprise a compact hourglass-shaped central region and a pair of precessing
jet-like structures. Time-resolved spectroscopy of its central star reveals
periodic radial velocity variability consistent with a binary system. While the
data are insufficient to accurately determine the parameters of the binary, the
most likely solutions indicate that the secondary is probably a low-mass main
sequence star. An empirical analysis of the chemical abundances in IC 4776
indicates that the common-envelope phase may have cut short the AGB evolution
of the progenitor. Abundances calculated from recombination lines are found to
be discrepant by a factor of approximately two relative to those calculated
using collisionally excited lines, suggesting a possible correlation between
low abundance discrepancy factors and intermediate-period post-common-envelope
central stars and/or Wolf-Rayet central stars. The detection of a radial
velocity variability associated with binarity in the central star of IC 4776
may be indicative of a significant population of (intermediate-period)
post-common-envelope binary central stars which would be undetected by classic
photometric monitoring techniques.Comment: Accepted for publication in MNRA
The impact of strong recombination on temperature determination in planetary nebulae
The long-standing difference in chemical abundances determined from optical
recombination lines and collisionally excited lines raises questions about our
understanding of atomic physics, as well as the assumptions made when
determining physical conditions and chemical abundances in astrophysical
nebulae. Here, we study the recombination contribution of [O III] 4363 and the
validity of the line ratio [O III] 4363/4959 as a temperature diagnostic in
planetary nebulae with a high abundance discrepancy. We derive a fit for the
recombination coefficient of [O III] 4363 that takes into account the radiative
and dielectronic recombinations, for electron temperatures from 200 to 30,000
K. We estimate the recombination contribution of [O III] 4363 for the planetary
nebulae Abell 46 and NGC 6778 by subtracting the collisional contribution from
the total observed flux. We find that the spatial distribution for the
estimated recombination contribution in [O III] 4363 follows that of the O II
4649 recombination line, both peaking in the central regions of the nebula,
especially in the case of Abell 46 which has a much higher abundance
discrepancy. The estimated recombination contribution reaches up to 70% and 40%
of the total [O III] 4363 observed flux, for Abell 46 and NGC 6778,
respectively.Comment: Accepted in MNRAS Letter
On the computation of interstellar extinction in photoionized nebulae
Ueta & Otsuka (2021) proposed a method, named as the "Proper Plasma Analysis
Practice", to analyze spectroscopic data of ionized nebulae. The method is
based on a coherent and simultaneous determination of the reddening correction
and physical conditions in the nebulae. The same authors (Ueta & Otsuka 2022,
UO22) reanalyzed the results of Galera-Rosillo et al. (2022, GR22) on nine of
the brightest planetary nebulae in M31. They claim that, if standard values of
the physical conditions are used to compute the extinction instead of their
proposed method, extinction correction is underestimated by more than 50% and
hence, ionic and elemental abundance determinations, especially the N/O ratio,
are incorrect. Several tests were performed to assess the accuracy of the
results of GR22, when determining: i) the extinction coefficient, ii) the
electron temperature and density, and iii) the ionic abundances. In the latter
case, N+ /H+ ionic abundance was recalculated using both H_alpha and H_beta as
the reference H I emissivity. The analysis shows that the errors introduced by
adopting standard values of the plasma conditions by GR22 are small, within
their quoted uncertainties. On the other hand, the interstellar extinction in
UO22 is found to be overestimated for five of the nine nebulae considered. This
propagates into their analysis of the properties of the nebulae and their
progenitors. The python notebook used to generate all the results presented in
this paper are of public access on a Github repository. The results from GR22
are proven valid and the conclusions of the paper hold firmly. Although the
PPAP is, in principle, a recommended practice, we insist that it is equally
important to critically assess which H I lines are to be included in the
determination of the interstellar extinction coefficient, and to assert that
physical results are obtained for the undereddened line ratios.Comment: Accepted for publication in A&A Lette
Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in √s=13 TeV pp collisions with the ATLAS detector
A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell W and Z bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of √s=13 TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb−1. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015–2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full data set are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at the 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV
Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at √ s = 8 TeV with the ATLAS detector
Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb−1 of √ s = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between Emiss T > 150 GeV and Emiss T > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presente
Observational Constraints on the Common Envelope Phase
The common envelope phase was first proposed more than forty years ago to
explain the origins of evolved, close binaries like cataclysmic variables. It
is now believed that the phase plays a critical role in the formation of a wide
variety of other phenomena ranging from type Ia supernovae through to binary
black holes, while common envelope mergers are likely responsible for a range
of enigmatic transients and supernova imposters. Yet, despite its clear
importance, the common envelope phase is still rather poorly understood. Here,
we outline some of the basic principles involved, the remaining questions as
well as some of the recent observational hints from common envelope phenomena -
namely planetary nebulae and luminous red novae - which may lead to answering
these open questions.Comment: 29 pages, 8 figures. To appear in the book "Reviews in Frontiers of
Modern Astrophysics: From Space Debris to Cosmology" (eds. Kabath, Jones and
Skarka; publisher Springer Nature) funded by the European Union Erasmus+
Strategic Partnership grant "Per Aspera Ad Astra Simul"
2017-1-CZ01-KA203-03556
- …