54 research outputs found
Mass distribution for single-lined hot subdwarf stars in LAMOST
Masses for 664 single-lined hot subdwarf stars identified in LAMOST were
calculated by comparing synthetic fluxes from spectral energy distribution
(SED) with observed fluxes from virtual observatory service. Three groups of
hot subdwarf stars were selected from the whole sample according to their
parallax precision to study the mass distributions. We found, that He-poor
sdB/sdOB stars present a wide mass distribution from 0.1 to 1.0
with a sharp mass peak around at 0.46 ,
which is consistent with canonical binary model prediction. He-rich
sdB/sdOB/sdO stars present a much flatter mass distribution than He-poor
sdB/sdOB stars and with a mass peak around 0.42 . By
comparing the observed mass distributions to the predictions of different
formation scenarios, we concluded that the binary merger channel, including two
helium white dwarfs (He-WDs) and He-WD + main sequence (MS) merger, cannot be
the only main formation channel for He-rich hot subdwarfs, and other formation
channels such as the surviving companions from type Ia supernovae (SNe Ia)
could also make impacts on producing this special population, especially for
He-rich hot subdwarfs with masses less than 0.44 . He-poor
sdO stars also present a flatter mass distribution with an inconspicuous peak
mass at 0.18 . The similar mass -
distribution between He-poor sdB/sdOB and sdO stars supports the scenario that
He-poor sdO stars could be the subsequent evolution stage of He-poor sdB/sdOB
stars.Comment: 38 pages, 13 figures, 3 tables, accepted for publication in Ap
Hot subdwarf stars identified in LAMOST DR8 with single-lined and composite spectra
222 hot subdwarf stars were identified with LAMOST DR8 spectra, among which
131 stars show composite spectra and have been decomposed, while 91 stars
present single-lined spectra. Atmospheric parameters of all sample stars were
obtained by fitting Hydrogen (H) and Helium (He) line profiles with synthetic
spectra. Two long-period composite sdB binaries were newly discovered by
combining our sample with the non-single star data from Gaia DR3. One of the
new systems presents the highest eccentricity (i.e., 0.5 +/- 0.09) among known
wide sdB binaries, which is beyond model predictions. 15 composite sdB stars
fall in the high probability binary region of RUWE-AEN plane, and deserve
priority follow-up observations to further study their binary nature. A
distinct gap is clearly presented among temperatures of cool companions for our
composite-spectra sample. But we could not come to a conclusion whether this
feature is connected to the formation history of hot subdwarf stars before
their binary natures are confirmed.Comment: 21 pages, 11 figures, 3 tables, Accepted for publication in Ap
Birthrates and delay times of Type Ia supernovae
Type Ia supernovae (SNe Ia) play an important role in diverse areas of
astrophysics, from the chemical evolution of galaxies to observational
cosmology. However, the nature of the progenitors of SNe Ia is still unclear.
In this paper, according to a detailed binary population synthesis study, we
obtained SN Ia birthrates and delay times from different progenitor models, and
compared them with observations. We find that the Galactic SN Ia birthrate from
the double-degenerate (DD) model is close to those inferred from observations,
while the birthrate from the single-degenerate (SD) model accounts for only
about 1/2-2/3 of the observations. If a single starburst is assumed, the
distribution of the delay times of SNe Ia from the SD model is a weak
bimodality, where the WD + He channel contributes to the SNe Ia with delay
times shorter than 100Myr, and the WD + MS and WD + RG channels to those with
age longer than 1Gyr.Comment: 11 pages, 2 figures, accepted by Science in China Series G (Dec.30,
2009
Immunity and clinical efficacy of an inactivated enterovirus 71 vaccine in healthy Chinese children: a report of further observations
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