747 research outputs found
Spectrum Analysis of the Type Ib Supernova 1999dn: Probable Identifications of C II and H-alpha
Low resolution spectra of SN 1999dn at early times are presented and compared
with synthetic spectra generated with the parameterized supernova
synthetic-spectrum code SYNOW. We find that the spectra of SN 1999dn strongly
resemble those of SN 1997X and SN 1984L, and hence we classify it as a Type Ib
event. Line-identifications are established through spectrum synthesis. Strong
evidence of both H-alpha and C II 6580 is found. We infer that H-alpha appears
first, before the time of maximum brightness, and then is blended with and
finally overwhelmed by the C II line after maximum; this favors a thin
high-velocity hydrogen skin in this Type Ib supernova.Comment: 15 pages, 3 figures. Accepted for publication in Ap
Discovery of the first symbiotic star in NGC6822
We report the discovery of the first symbiotic star (V=21.6, K_S=15.8 mag) in
the Local Group dwarf irregular galaxy NGC6822. This star was identified during
a spectral survey of Ha emission-line objects using the Southern African Large
Telescope (SALT) during its performance-verification phase. The observed strong
emission lines of HI and HeII suggest a high electron density and T* < 130 000
K for the hot companion. The infrared colours allow us to classify this object
as an S-type symbiotic star, comprising a red giant losing mass to a compact
companion. The red giant is an AGB carbon star, and a semi-regular variable,
pulsating in the first overtone with a period of 142 days. Its bolometric
magnitude is M_bol=-4.4 mag.
We review what is known about the luminosities of extragalactic symbiotic
stars, showing that most, possibly all, contain AGB stars. We suggest that a
much larger fraction of Galactic symbiotic stars may contain AGB stars than was
previously realised.Comment: 6 pages, 4 figures, accepted to MNRA
Macrophytes: A temporary sink for microplastics in transitional water systems
Marine macrophytes are hypothesized to be a major temporary sink for microplastics. In this study, microplastic contamination was investigated in 15 macroalgal species and one seagrass from different sites in two lagoons of the northern Adriatic Sea: the Goro lagoon and the Venice lagoon. A high percentage (94%) of the macrophyte samples contained microplastics, ranging from 0.16 to 330 items gâ1 fw, with the prevalent size in the range 30â90 ”m and an average contamination per unit of fresh weight of 14 items gâ1 fw. Microplastic contamination displayed a site-specific, rather than a species-specific, pattern of accumulation. In addition, exopolysaccharides (EPS) displayed a significant positive correlation with the microplastics ononcontamination on macrophytes acting as glue for the plastic particles available in the water column
Sedimentation Rates: Anthropogenic Impacts and Environmental Changes in Transitional Water Systems
The trophic evolution of the Venice lagoon was analyzed by studying the particulate collected monthly with sedimentation traps in many areas of the Venice lagoon since 1989, and at Goro in 2018â2019. Sedimentation rates were strongly related to the presence of macrophytes, which reduced sediment resuspension, and to anthropogenic pressures, such as clam harvesting and naval-boat traffic, that triggered sediment resuspension and loss. The highest mean annual sedimentation rates (from 2000 to over 4000 g DWT mâ2 dayâ1) have been recorded in many areas of the Venice lagoon between 1998â1999 to 2001â2002, during the intense fishing activities of the clam Ruditapes philippinarum. High values (daily peaks up to 5224 g DWT mâ2 dayâ1) were also recorded in areas affected by marine and/or recreational traffic, due to the high wave motion. In contrast, the presence of high biomasses of macroalgae, or seagrasses, reduced significantly sediment resuspension and settlement, with mean annual sedimentation rates ranging between 40 and 140 g DWT mâ2 dayâ1 and minimum values of 6â10 g DWT mâ2 dayâ1. High sedimentation rates were strongly related to a lower sediment grain-size, with loss of the fine fraction and dispersion of nutrients and pollutants in the whole lagoon
Optical evolution of Nova Ophiuchi 2007 = V2615 Oph
The moderately fast Nova Oph 2007 reached maximum brightness on March 28,
2007 at V=8.52, B-V=+1.12, V-Rc=+0.76, V-Ic=+1.59 and Rc-Ic=+0.83, after fast
initial rise and a pre-maximum halt lasting a week. Decline times were
t(V,2)=26.5, t(B,2)=30, t(V,3)=48.5 and t(B,3)=56.5 days. The distance to the
nova is d=3.7 kpc, the height above the galactic plane z=215 pc, the reddening
E(B-V)=0.90 and the absolute magnitude at maximum M(V,max)=-7.2 and
M(B,max)=-7.0. The spectrum four days before maximum resembled a F6
super-giant, in agreement with broad-band colors. It later developed into that
of a standard 'FeII'-class nova. Nine days past maximum, the expansion velocity
estimated from the width of H emission component was 730 km/s, and the
displacement from it of the principal and diffuse enhanced absorption systems
were 650 and 1380 km/s, respectively. Dust probably formed and disappeared
during the period from 82 to 100 days past maximum, causing (at peak dust
concentration) an extinction of Delta B=1.8 mag and an extra Delta E(B-V)=0.44
reddening.Comment: accepted in press by MNRA
Repetibilidade da idade ao primeiro parto, intervalo de partos e peso ao parto em bovinos da Rraça Nelore.
Utilizaram-se 407 observaçÔes de idade ao primeiro parto, 971 de intervalo de partos e 587 de peso ao parto de vacas da raça Nelore, para avaliar os efeitos de alguns fatores sobre essas caracterĂsticas e estimar seus coeficientes de repetibilidade
Helium Emission in the Type Ic SN 1999cq
We present the first unambiguous detection of helium emission lines in
spectra of Type Ic supernovae (SNe Ic). The presence of He I lines, with full
width at half maximum ~ 2000 km/s, and the distinct absence of any other
intermediate-width emission (e.g., Halpha), implies that the ejecta of SN Ic
1999cq are interacting with dense circumstellar material composed of almost
pure helium. This strengthens the argument that the progenitors of SNe Ic are
core-collapse events in stars that have lost both their hydrogen and helium
envelopes, either through a dense wind or mass-transfer to a companion. In this
way, SN 1999cq is similar to supernovae such as SN 1987K and SN 1993J that
helped firmly establish a physical connection between Type Ib and Type II
supernovae. The light curve of SN 1999cq is very fast, with an extremely rapid
rise followed by a quick decline. SN 1999cq is also found to exhibit a high
level of emission at blue wavelengths (< 5500 A), likely resulting from either
an unusually large amount of iron and iron-group element emission or
uncharacteristically low reddening compared with other SNe Ic.Comment: 17 pages (AASTeX V5.0), 4 figures, accepted for publication in the
Astronomical Journa
FLAMES spectroscopy of low-mass stars in the young clusters sigma Ori and lambda Ori
Aims. We performed a detailed membership selection and studied the accretion
properties of low-mass stars in the two apparently very similar young (1-10
Myr) clusters sigma Ori and lambda Ori.
Methods. We observed 98 and 49 low-mass (0.2-1.0 M_sun) stars in sigma Ori
and lambda Ori respectively, using the multi-object optical spectrograph FLAMES
at the VLT, with the high-resolution (R=17,000) HR15N grating (6470-6790 AA).
We used radial velocities, Li and Halpha to establish cluster membership and
Halpha and other optical emission lines to analyze the accretion properties of
members.
Results. We identified 65 and 45 members of the sigma Ori and lambda Ori
clusters, respectively and discovered 16 new candidate binary systems. We also
measured rotational broadening for 20 stars and estimated the mass accretion
rates in 25 stars of the sigma Ori cluster, finding values between 10^-11 and
10^-7.7 M_sun yr^-1 and in 4 stars of the lambda Ori cluster, finding values
between 10^-11 and 10^-10.1 M_sun yr-1. Comparing our results with the infrared
photometry obtained by the Spitzer satellite, we find that the fraction of
stars with disks and the fraction of active disks is larger in the sigma Ori
cluster (52+-9% and 78+-16%) than in lambda Ori (28+-8% and 40+-20%)
Conclusions. The different disk and accretion properties of the two clusters
could be due either to the effect of the high-mass stars and the supernova
explosion in the lambda Ori cluster or to different ages of the cluster
populations. Further observations are required to draw a definitive conclusion.Comment: 14 pages, 9 figures, 9 tables, accepted for publications in A&
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