79 research outputs found
Tomographic separation of composite spectra. The components of Plaskett's Star
The UV photospheric lines of Plaskett's Star (HD 47129), a 14.4 day period, double lined O-type spectroscopic binary were analyzed. Archival data from IUE (17 spectra well distributed in orbital phase) were analyzed with several techniques. A cross correlation analysis, which showed that the secondary produces significant lines in the UV, indicates that the mass ratio is q = 1.18 + or - 0.12 (secondary slightly more massive). A tomography algorithm was used to produce the separate spectra of the two stars in six spectral regions. The interpolated spectral classifications of the primary and secondary, 07.3 I and 06.2 I, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. The intensity ratio of the stars in the UV is 0.53 + or - 0.05 (primary brighter). The secondary lines appear rotationally broadened, and the projected rotational velocity V sin i for this star is estimated to be 310 + or - 20 km/s. The possible evolutionary history of this system is discussed through a comparison of the positions of the components and evolutionary tracks in the H-R diagram
Use of microbial fuel cells for soil remediation. A preliminary study on DDE
DDE (2,2-bis (p-chlorophenyl)-1,1-dichloroetylene) is a very persistent and bioaccumulative pesticide and its residues are continuously found in the environment. Among the green remediation strategies for soil recovery, terrestrial Microbial Fuel Cells (MFC) are arousing great interest in scientific community. MFCs transform energy stored in the chemical bonds of organic compounds into electrical energy thanks to exo-electrogen microorganisms naturally occurring in soil, which catalyse oxidation and reduction reactions in the area between two graphite electrodes. This work reports preliminary data on the use of MFCs for promoting soil decontamination from DDE. Several experimental conditions (e.g. addition of compost and open/closed circuit) were applied for assessing how to improve MFC performance in favouring DDE removal. MFCs promoted a significant DDE removal (39%) after 2 months, while at the same time any pesticide decrease was observed in the batch condition. Compost addition stimulated microbial activity and improved MFC performance for a longer time
The Struve-Sahade effect in the optical spectra of O-type binaries I. Main-sequence systems
We present a spectroscopic analysis of four massive binary systems that are
known or are good candidates to display the Struve-Sahade effect (defined as
the apparent strengthening of the secondary spectrum of the binary when the
star is approaching, and the corresponding weakening of the lines when it is
receding).
We use high resolution optical spectra to determine new orbital solutions and
spectral types of HD 165052, HD 100213, HD 159176 and DH Cep. As good knowledge
of the fundamental parameters of the considered systems is necessary to examine
the Struve-Sahade effect. We then study equivalent width variations in the
lines of both components of these binaries during their orbital cycle.
In the case of these four systems, variations appear in the equivalent widths
of some lines during the orbital cycle, but the definition given above can any
longer be valid, since it is now clear that the effect modifies the primary
spectrum as much as the secondary spectrum. Furthermore, the lines affected,
and the way in which they are affected, depend on the considered system. For at
least two of them (HD 100213 and HD 159176) these variations probably reflect
the ellipsoidal variable nature of the system.Comment: 12 pages, 20 figures, in press A&
High resolution optical spectroscopy of Plaskett's star
We present here the analysis of an extensive set of high resolution optical
spectra of Plaskett's star (HD 47129). We use a disentangling method to
separate the individual spectra of each star. We derive a new orbital solution
and discuss the spectral classification of both components. A Doppler
tomography technique applied to the emission lines H alpha and He II 4686
yields a Doppler map that illustrates the wind interactions in the system.
Finally, an atmosphere code is used to determine the different chemical
abundances of the system components and the wind parameters. HD 47129 appears
to be an O8 III/I + O7.5 III binary system in a post RLOF evolutionary stage,
where matter has been transferred from the primary to the secondary star. The
He overabundance of the secondary supports this scenario. In addition, the N
overabundance and C underabundance of the primary component confirm previous
results based on X-ray spectroscopy and indicate that the primary is an evolved
massive star. Furthermore, the secondary star has a large rotational velocity
that deforms its surface, leading to a non-uniform distribution in effective
temperature. This could explain the variations in the equivalent widths of the
secondary lines with phase. We suggest that the wind of the secondary star is
confined near the equatorial plane because of its high rotational velocity,
affecting the ram pressure equilibrium in the wind interaction zone.Comment: Accepted in A &
Tomographic Separation of Composite Spectra. VIII. The Physical Properties of the Massive Compact Binary in the Triple Star System HD 36486 (delta Orionis A)
Double-lined spectroscopic orbital elements have recently been found for the
central binary in the massive triple, delta Orionis A based on radial
velocities from cross-correlation techniques applied to IUE high dispersion
spectra and He I 6678 spectra obtained at Kitt Peak. The primary and secondary
velocity amplitudes were found to be 94.9 +/- 0.6 km/s and 186 +/- 9 km/s
respectively. Tomographic reconstructions of the primary and secondary stars'
spectra confirm the O9.5 II classification of the primary and indicate a B0.5
III type for the secondary. The widths of the UV cross-correlation functions
are used to estimate the projected rotational velocities, Vsin i = 157 +/- 6
km/s and 138 +/- 16 km/s for the primary and secondary, respectively implying
that both stars rotate faster than their orbital motion. We used the
spectroscopic results to make a constrained fit of the Hipparcos light curve of
this eclipsing binary, and the model fits limit the inclination to the range
between 67 and 77 degrees. The i = 67 degrees solution, which corresponds to a
near Roche-filling configuration, results in a primary mass of 11.2 solar
masses and a secondary mass of 5.6 solar masses, both of which are
substantially below the expected masses for stars of their luminosity. This
binary may have experienced a mass ratio reversal caused by Case A Roche lobe
overflow, or the system may have suffered extensive mass loss through a binary
interaction, perhaps during a common envelope phase, in which most of the
primary's mass was lost from the system rather than transferred to the
secondary.Comment: 27 pages, 15 figures in press, the Astrophysical Journal, February 1,
200
First Results from the CHARA Array. II. A Description of the Instrument
The CHARA Array is a six 1-m telescope optical/IR interferometric array
located on Mount Wilson California, designed and built by the Center for High
Angular Resolution Astronomy of Georgia State University. In this paper we
describe the main elements of the Array hardware and software control systems
as well as the data reduction methods currently being used. Our plans for
upgrades in the near future are also described
HD 62454 and HD 68192: Two New γ Doradus Variables
We present multilongitude, multicolor photometry and simultaneous high-resolution, high signal-to-noise spectroscopy of the newly discovered γ Doradus variables HD 62454 and HD 68192. From combined Johnson and Strömgren data, we are able to identify five independent periods in HD 62454 and two stable periods in HD 68192. The data presented are sufficient to rule out all physically meaningful types of variations, with the one exception of the high-order, low-degree, nonradial gravity-mode pulsations that are believed to be at work in γ Doradus stars. We also find that HD 62454 is a double-lined spectroscopic binary and we present an orbital solution
Early-type stars in the young open cluster IC1805. II. The probably single stars HD15570 and HD15629, and the massive binary/triple system HD15558
Aims: We address the issue of the multiplicity of the three brightest
early-type stars of the young open cluster IC1805, namely HD15570, HD15629 and
HD15558. Methods: For the three stars, we measured the radial velocity by
fitting Gaussian curves to line profiles in the optical domain. In the case of
the massive binary HD15558, we also used a spectral disentangling method to
separate the spectra of the primary and of the secondary in order to derive the
radial velocities of the two components. These measurements were used to
compute orbital solutions for HD15558. Results: For HD15570 and HD15629, the
radial velocities do not present any significant trend attributable to a binary
motion on time scales of a few days, nor from one year to the next. In the case
of HD15558 we obtained an improved SB1 orbital solution with a period of about
442 days, and we report for the first time on the detection of the spectral
signature of its secondary star. We derive spectral types O5.5III(f) and O7V
for the primary and the secondary of HD15558. We tentatively compute a first
SB2 orbital solution although the radial velocities from the secondary star
should be considered with caution. The mass ratio is rather high, i.e. about 3,
and leads to very extreme minimum masses, in particular for the primary object.
Minimum masses of the order of 150 \pm 50 and 50 \pm 15 M_\odot are found
respectively for the primary and the secondary. Conclusions: We propose that
HD15558 could be a triple system. This scenario could help to reconcile the
very large minimum mass derived for the primary object with its spectral type.
In addition, considering new and previously published results, we find that the
binary frequency among O-stars in IC1805 has a lower limit of 20%, and that
previously published values (80%) are probably overestimated.Comment: 12 pages, including 6 figures (+ 4 pages of online material),
accepted for publication by A&
A Spectroscopic Orbit for Regulus
We present a radial velocity study of the rapidly rotating B-star Regulus
that indicates the star is a single-lined spectroscopic binary. The orbital
period (40.11 d) and probable semimajor axis (0.35 AU) are large enough that
the system is not interacting at present. However, the mass function suggests
that the secondary has a low mass (M_2 > 0.30 M_sun), and we argue that the
companion may be a white dwarf. Such a star would be the remnant of a former
mass donor that was the source of the large spin angular momentum of Regulus
itself.Comment: 18 pages, 2 figures, ApJL in pres
Surprising dissimilarities in a newly formed pair of 'identical twin' stars
The mass and chemical composition of a star are the primary determinants of
its basic physical properties--radius, temperature, luminosity--and how those
properties evolve with time. Thus, two stars born at the same time, from the
same natal material, and with the same mass are 'identical twins,' and as such
might be expected to possess identical physical attributes. We have discovered
in the Orion Nebula a pair of stellar twins in a newborn binary star system.
Each star in the binary has a mass of 0.41 +/- 0.01 solar masses, identical to
within 2 percent. Here we report that these twin stars have surface
temperatures that differ by ~300K (~10%), and luminosities that differ by ~50%,
both at high confidence level. Preliminary results indicate that the stars'
radii also differ, by 5-10%. These surprising dissimilarities suggest that one
of the twins may have been delayed by several hundred thousand years in its
formation relative to its sibling. Such a delay could only have been detected
in a very young, definitively equal-mass binary system3 such as that reported
here. Our findings reveal cosmic limits on the age synchronisation of young
binary stars, often used as tests for the age calibrations of star-formation
models.Comment: Published in Nature, 19 June 200
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