1,709 research outputs found
The SMC X-ray transient XTE J0111.2-7317 : a Be/X-ray binary in a SNR?
We report observations which confirm the identity of the optical/IR
counterpart to the Rossi X-ray Timing Explorer transient source XTE
J0111.2-7317. The counterpart is suggested to be a B0-B2 star (luminosity class
III--V) showing an IR excess and strong Balmer emission lines. The distance
derived from reddening and systemic velocity measurements puts the source in
the SMC. Unusually, the source exhibits an extended asymetric H alpha
structure.Comment: 5 pages, 3 figs, accepted by MNRA
The nature of 1WGA J1958.2+3232: a new intermediate polar
We present low and intermediate resolution spectroscopy of the optical counterpart to the recently discovered pulsating X-ray source 1WGA J1958.2+3232. The presence of strong HI , HeI and HeII emission lines together with the absence of absorption features rules out the possibility that the object is a massive star, as had recently been suggested. The observed X-ray and optical characteristics are consistent with the object being an intermediate polar. The double-peaked structure of the emission lines indicates that an accretion disc is present
Calculating shadow wages for family labour in agriculture : An analysis for Spanish citrus fruit farms
This paper deals with the calculation of shadow wages for family labour in agriculture. Using the existence of a duality between input distance and cost functions, we use the former to derive individual labour shadow prices for a sample of Spanish citrus fruit producers. Our results show that the average shadow price representing the opportunity cost of family labour employed onfarm, is lower than the average market wage rate paid for hired labour. We relate this finding to a strategy of outsourcing of many growing tasks that is currently pursued by farmers to overcome the problems posed by a suboptimal farm size.shadow prices, duality, distance functions, on-farm labour opportunity cost, outsourcing
Sobre la posición sistemática del género Placogyropsis Alloiteau, 1957. (Scleractinia cretácica)
Utilizando varios topotipos de la especie tipo, se estudia el género Placogyropsis Alloiteau, 1957, inscrito por el propio Alloiteau en la familia Dendrogyriidae Alloiteau, 1952. Se sugiere que no pertenece a esta familia, sino a la familia Latomeandriidae y se propone una diagnosis del género
A 0535+26: Back in business
In May/June 2005, after 10 years of inactivity, the Be/X-ray binary system A
0535+26 underwent a major X-ray outburst. In this paper data are presented from
10 years of optical, IR and X-ray monitoring showing the behaviour of the
system during the quiescent epoch and the lead up to the new outburst. The
results show the system going through a period when the Be star in the system
had a minimal circumstellar disk and then a dramatic disk recovery leading,
presumably, to the latest flare up of X-ray emission. The data are interpreted
in terms of the state of the disk and its interaction with the neutron star
companion.Comment: Accepted for publication in MNRA
Sobre la posición sistemática del género Placogyropsis Alloiteau, 1957. (Scleractinia cretácica)
Utilizando varios topotipos de la especie tipo, se estudia el género Placogyropsis Alloiteau, 1957, inscrito por el propio Alloiteau en la familia Dendrogyriidae Alloiteau, 1952. Se sugiere que no pertenece a esta familia, sino a la familia Latomeandriidae y se propone una diagnosis del género
Bound-state dark matter with Majorana neutrinos
We propose a simple scenario in which dark matter (DM) emerges as a stable
neutral hadronic thermal relics, its stability following from an exact
symmetry. Neutrinos pick up radiatively induced
Majorana masses from the exchange of colored DM constituents. There is a common
origin for both dark matter and neutrino mass, with a lower bound for
neutrinoless double beta decay. Direct DM searches at nuclear recoil
experiments will test the proposal, which may also lead to other
phenomenological signals at future hadron collider and lepton flavour violation
experiments.Comment: 9 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1803.0852
Long-term variability of high-mass X-ray binaries. I.Photometry
We present photometric observations of the field around the optical
counterparts of high-mass X-ray binaries. Our aim is to study the long-term
photometric variability in correlation with their X-ray activity and derive a
set of secondary standard stars that can be used for time series analysis. We
find that the donors in Be/X-ray binaries exhibit larger amplitude changes in
the magnitudes and colours than those hosting a supergiant companion. The
amplitude of variability increases with wavelength in Be/X-ray binaries and
remains fairly constant in supergiant systems. When time scales of years are
considered, a good correlation between the X-ray and optical variability is
observed. The X-rays cease when optical brightness decreases. These results
reflect the fact that the circumstellar disk in Be/X-ray binaries is the main
source of both optical and X-ray variability. We also derive the colour excess,
E(B-V), selecting data at times when the contribution of the circumstellar disk
was supposed to be at minimum, and we revisit the distance estimates
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