38 research outputs found
The magnetic field of the B3V star 16 Pegasi
The Slowly Pulsating B3V star 16 Pegasi was discovered by Hubrig (2006) to be
magnetic, based on low-resolution spectropolarimetric observations with FORS1
at the VLT. We have confirmed the presence of a magnetic field with new
measurements with the spectropolarimeters Narval at TBL, France and Espadons at
CFHT, Hawaii during 2007. The most likely period is about 1.44 d for the
modulation of the field, but this could not be firmly established with the
available data set. No variability has been found in the UV stellar wind lines.
Although the star was reported once to show H alpha in emission, there exists
at present no confirmation that the star is a Be star.Comment: 2 pages, 4 figures, contrubuted poster at IAU Symposium 259 "Cosmic
Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain,
November 3-7, 200
A computational analysis of lower bounds for big bucket production planning problems
In this paper, we analyze a variety of approaches to obtain lower bounds for multi-level production planning problems with big bucket capacities, i.e., problems in which multiple items compete for the same resources. We give an extensive survey of both known and new methods, and also establish relationships between some of these methods that, to our knowledge, have not been presented before. As will be highlighted, understanding the substructures of difficult problems provide crucial insights on why these problems are hard to solve, and this is addressed by a thorough analysis in the paper. We conclude with computational results on a variety of widely used test sets, and a discussion of future research
Multisite spectroscopic seismic study of the beta Cep star V2052 Oph: inhibition of mixing by its magnetic field
We used extensive ground-based multisite and archival spectroscopy to derive
observational constraints for a seismic modelling of the magnetic beta Cep star
V2052 Ophiuchi. The line-profile variability is dominated by a radial mode
(f_1=7.14846 d^{-1}) and by rotational modulation (P_rot=3.638833 d). Two
non-radial low-amplitude modes (f_2=7.75603 d^{-1} and f_3=6.82308 d^{-1}) are
also detected. The four periodicities that we found are the same as the ones
discovered from a companion multisite photometric campaign (Handler et al.
2012) and known in the literature. Using the photometric constraints on the
degrees l of the pulsation modes, we show that both f_2 and f_3 are prograde
modes with (l,m)=(4,2) or (4,3). These results allowed us to deduce ranges for
the mass (M \in [8.2,9.6] M_o) and central hydrogen abundance (X_c \in
[0.25,0.32]) of V2052 Oph, to identify the radial orders n_1=1, n_2=-3 and
n_3=-2, and to derive an equatorial rotation velocity v_eq \in [71,75] km
s^{-1}. The model parameters are in full agreement with the effective
temperature and surface gravity deduced from spectroscopy. Only models with no
or mild core overshooting (alpha_ov \in [0,0.15] local pressure scale heights)
can account for the observed properties. Such a low overshooting is opposite to
our previous modelling results for the non-magnetic beta Cep star theta Oph
having very similar parameters, except for a slower surface rotation rate. We
discuss whether this result can be explained by the presence of a magnetic
field in V2052 Oph that inhibits mixing in its interior.Comment: 12 pages, 6 figures and 5 tables; accepted for publication in MNRAS
on 2012 August 1
On the incidence of magnetic fields in slowly-pulsating B, Beta Cephei and B-type emission line stars
We have obtained 40 high-resolution circular spectropolarimetric measurements
of 12 slowly-pulsating B (SPB) stars, 8 Beta Cephei stars and two Be stars with
the ESPaDOnS and NARVAL spectropolarimeters. The aim of these observations is
to evaluate recent claims of a high incidence of magnetic field detections in
stars of these types obtained using low-resolution spectropolarimetry by Hubrig
(2006), Hubrig (2007) and Hubrig (2009). The precision achieved is generally
comparable to or superior to that obtained by Hubrig et al., although our new
observations are distinguished by their resolution of metallic and He line
profiles, and their consequent sensitivity to magnetic fields of zero net
longitudinal component. In the SPB stars we confirm the detection of magnetic
field in one star (16 Peg), but find no evidence of the presence of fields in
the remaining 11. In the Beta Cep stars, we detect a field in xi^1 CMa, but not
in any of the remaining 7 stars. Finally, neither of the two B-type emission
line stars shows any evidence of magnetic field. Based on our results, we
conclude that fields are not common in SPB, Beta Cep and B-type emission line
stars, consistent with the general rarity of fields in the broader population
of main sequence B-type stars.Comment: Accepted - MNRA