23,399 research outputs found
A TiO study of the black-hole binary GRO J0422+32 in a very low state
We present 53 simultaneous photometric (I band) and spectroscopic (6900-9500
Angstroms) observations of J0422+32, taken during December 1997. From these we
determine that J0422+32 was in its lowest state yet observed, at
I=20.44+/-0.08. Using relative spectrophotometry, we show that it is possible
to correct very accurately for telluric absorption. Following this, we use the
TiO bands at 7055 Angstroms and 7589 Angstroms for a radial velocity study and
thereby obtain a semi-amplitude of 378+/-16kms-1, which yields
f(M)=1.191+/-0.021M_solar and q=9.0+2.2-2.7, consistent with previous
observations. We further demonstrate that this little explored method is very
powerful for such systems. We also determine a new orbital ephemeris of
HJD=2450274.4156+/-0.0009 + 0.2121600+/-0.0000002E.
We see some evidence for an ellipsoidal modulation, from which we determine
the orbital inclination of J0422+32 to be less than 45 degrees. We therefore
calculate a minimum mass for the primary of 2.22M_solar, consistent with a
black hole, but not necessarily the super-massive one proposed by Beekman et al
(1997). We obtain an M4-5 spectral type for the secondary star and determine
that the secondary contributes 38+/-2% of the flux that we observe from
J0422+32 over the range 6950-8400 Angstroms. From this we calculate the
distance to the system to be 1.39+/-0.15kpc.Comment: (1) Department of Physics, Keele University, Keele, Staffordshire,
ST5 5BG (2) Department of Astrophysics, Nuclear Physics Laboratory, Keble
Road, Oxfo rd, OX1 3RH Accepted, to appear in MNRAS 8 pages, 5 figure
Faint star counts in the near-infrared
We discuss near-infrared star counts at the Galactic pole with a view to
guiding the NGST and ground-based NIR cameras. Star counts from deep K-band
images from the CFHT are presented, and compared with results from the 2MASS
survey and some Galaxy models. With appropriate corrections for detector
artifacts and galaxies, the data agree with the models down to K~18, but
indicate a larger population of fainter red stars. There is also a significant
population of compact galaxies that extend to the observational faint limit of
K=20.5. Recent Galaxy models agree well down to K19, but diverge at
fainter magnitudes.Comment: 14 pages and 4 diagrams; to appear in PAS
A fourth HI 21-cm absorption system in the sight-line of MG J0414+0534: a record for intervening absorbers
We report the detection of a strong HI 21-cm absorption system at z=0.5344,
as well as a candidate system at z=0.3389, in the sight-line towards the z=2.64
quasar MG J0414+0534. This, in addition to the absorption at the host redshift
and the other two intervening absorbers, takes the total to four (possibly
five). The previous maximum number of 21-cm absorbers detected along a single
sight-line is two and so we suspect that this number of gas-rich absorbers is
in some way related to the very red colour of the background source. Despite
this, no molecular gas (through OH absorption) has yet been detected at any of
the 21-cm redshifts, although, from the population of 21-cm absorbers as a
whole, there is evidence for a weak correlation between the atomic line
strength and the optical--near-infrared colour. In either case, the fact that
so many gas-rich galaxies (likely to be damped Lyman-alpha absorption systems)
have been found along a single sight-line towards a highly obscured source may
have far reaching implications for the population of faint galaxies not
detected in optical surveys, a possibility which could be addressed through
future wide-field absorption line surveys with the Square Kilometre Array.Comment: Accepted by ApJ Letter
Relativistic effects in Ni II and the search for variation of the fine structure constant
Theories unifying gravity and other interactions suggest the possibility of
spatial and temporal variation of physical ``constants'' in the Universe.
Detection of high redshift absorption systems intersecting the sight lines
towards distant quasars provide a powerful tool for measuring these variations.
In the present paper we demonstrate that high sensitivity to variation of the
fine structure constant alpha can be obtained by comparing cosmic and
laboratory spectra of the Ni II ion. Relativistic effects in Ni II reveal many
interesting features. The Ni II spectrum exhibits avoided level crossing
phenomenon under variation of alpha and the intervals between the levels have
strong nonlinear dependencies on relativistic corrections. The values of the
transition frequency shifts, due to the change of alpha, vary significantly
from state to state including change of the sign. This enhances the sensitivity
to the variation of alpha and reduces possible systematic errors. The
calculations of alpha-dependence of the nickel ion spectral lines that are
detectable in quasar absorption spectra have been performed using a
relativistic configuration interaction method.Comment: 13 pages, 1 figure, accepted by Phys. Rev. A, typos corrected,
acknowledgment adde
Diffusive electron acceleration at SNR shock fronts and the observed SNR radio spectral indices
The radio synchrotron emission from relativistic electrons in shell supernova remnants (SNRs) provides a unique opportunity to probe the energy distribution of energetic electrons at their acceleration site (SNR shock fronts). This information provides insight into the acceleration mechanism(s). The implications of these observations for the diffusive (first-order Fermi) acceleration of electrons at the SNR shock fronts are discussed
Reports Of Conferences, Institutes, And Seminars
This quarter\u27s column offers coverage of multiple sessions from the 2016 Electronic Resources & Libraries (ER&L) Conference, held April 3–6, 2016, in Austin, Texas. Topics in serials acquisitions dominate the column, including reports on altmetrics, cost per use, demand-driven acquisitions, and scholarly communications and the use of subscriptions agents; ERMS, access, and knowledgebases are also featured
High spatial resolution observations of CUDSS14A: a SCUBA-selected ultraluminous galaxy at high redshift
The definitive version is available at www.blackwell-synergy.com '. Copyright Blackwell Publishing DOI : 10.1046/j.1365-8711.2000.03822.xWe present a high-resolutionmillimetre interferometric image of the brightest SCUBA- selected galaxy from the Canada-UK deep SCUBA survey (CUDSS). We make a very clear detection at 1.3 mm, but fail to resolve any structure in the source.Peer reviewe
An integrated approach for analysing and assessing the performance of virtual learning groups
Collaborative distance learning involves a variety of elements and factors that have to be considered and measured in order to analyse and assess group and individual performance more effectively and objectively. This paper presents an approach that integrates qualitative, social network analysis (SNA) and quantitative techniques for evaluating online collaborative learning interactions. Integration of various different data sources, tools and techniques provides a more complete and robust framework for group modelling and guarantees a more efficient evaluation of group effectiveness and individual competence. Our research relies on the analysis of a real, long-term, complex collaborative experience, which is initially evaluated in terms of principled criteria and a basic qualitative process. At the end of the experience, the coded student interactions are further analysed through the SNA technique to assess participatory aspects, identify the most effective groups and the most prominent actors. Finally, the approach is contrasted and completed through a statistical technique which sheds more light on the results obtained that far. The proposal draws a well-founded line toward the development of a principled framework for the monitoring and analysis of group interaction and group scaffolding which can be considered a major issue towards the actual application of the CSCL proposals to real classrooms.Peer ReviewedPostprint (author's final draft
A SCUBA Map in the Spitzer First Look Survey: Source Catalog and Number Counts
Using the SCUBA instrument on the JCMT, we have made a submillimeter mosaic
at 850um of a subarea of the Spitzer First Look Survey (FLS). Our image covers
the central 151 square arcmin of the northern extragalactic Continuous Viewing
Zone (CVZ) field of the FLS to a median 3sigma depth of 9.7 mJy. The image
contains ten 850um sources detected at 3.5sigma or higher significance, of
which five are detected at greater than or equal 4sigma. We make the catalog of
these SCUBA-selected FLS sources available to the community. After correcting
for incompleteness and flux bias, we find that the density of sources brighter
that 10mJy in our field is (1.3 +1.1 -0.7)x10^2 deg^-2 (95% Poisson confidence
limits), which is consistent with other surveys that probe the bright end of
the submillimeter population.Comment: ApJL, in press. Higher quality versions of Figs 1 and 3 can be
obtained from the author
Big bang nucleosynthesis as a probe of fundamental "constants"
Big Bang nucleosynthesis (BBN) is the earliest sensitive probe of the values
of many fundamental particle physics parameters. We have found the leading
linear dependences of primordial abundances on all relevant parameters of the
standard BBN code, including binding energies and nuclear reaction rates. This
enables us to set limits on possible variations of fundamental parameters. We
find that 7Li is expected to be significantly more sensitive than other species
to many fundamental parameters, a result which also holds for variations of
coupling strengths in grand unified (GUT) models. Our work also indicates which
areas of nuclear theory need further development if the values of ``constants''
are to be more accurately probed.Comment: Refereed article to be published in Nuclear Physics in Astrophysics
III Proceedings, J. Phys. G. Special Issue. Based on work in collaboration
with C. Wetterich (Heidelberg). 6 page
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