68 research outputs found
Gaia space mission and quasars
Quasars are often considered to be point-like objects. This is largely true
and allows for an excellent alignment of the optical positional reference frame
of the ongoing ESA mission Gaia with the International Celestial Reference
Frame. But presence of optical jets in quasars can cause shifts of the optical
photo-centers at levels detectable by Gaia. Similarly, motion of emitting blobs
in the jet can be detected as proper motion shifts. Gaia's measurements of
spectral energy distribution for around a million distant quasars is useful to
determine their redshifts and to assess their variability on timescales from
hours to years. Spatial resolution of Gaia allows to build a complete magnitude
limited sample of strongly lensed quasars. The mission had its first public
data release in September 2016 and is scheduled to have the next and much more
comprehensive one in April 2018. Here we briefly review the capabilities and
current results of the mission. Gaia's unique contributions to the studies of
quasars are already being published, a highlight being a discovery of a number
of quasars with optical jets.Comment: Proceedings of the conference "Quasars at all cosmic epochs", Padova,
april 2017, Editors Chony del Olmo, Mauro D'Onofrio, Deborah Dultzin, Paola
Marziani. Published in Frontiers in Astronomy and Space Sciences, section
Milky Way and Galaxies, id30615
A high resolution, multi-epoch spectral atlas of peculiar stars including RAVE, GAIA and HERMES wavelength ranges
We present an Echelle+CCD, high S/N, high resolution (R = 20\,000)
spectroscopic atlas of 108 well-known objects representative of the most common
types of peculiar and variable stars. The wavelength interval extends from 4600
to 9400 Ang, and includes the RAVE, Gaia and HERMES wavelength ranges.
Multi-epoch spectra are provided for the majority of observed stars. A total of
425 spectra of peculiar stars are presented, which have been collected during
56 observing nights between November 1998 and August 2002. The spectra are
given in FITS format and heliocentric wavelengths, with accurate subtraction of
both the sky background and the scattered light. Auxiliary material useful for
custom applications (telluric dividers, spectro-photometric stars, flat-field
tracings) is also provided. The atlas aims to provide a homogeneous database of
the spectral appearance of stellar peculiarities, a tool useful both for
classification purposes and inter-comparison studies. It could also serve the
planning for and training of automated classification algorithms designed for
RAVE, Gaia, HERMES and other large scale spectral surveys. The spectrum of XX
Oph is discussed in some detail as an example of the content of the present
atlas.Comment: AJ in press (issue 140:6 December 2010
Optical Spectrum of Main-, Inter- and Off-pulse Emission from Crab Pulsar
A dedicated stroboscopic device was used to obtain optical spectra of the
Crab main-pulse and inter-pulse as well as the spectrum of the underlying
nebula when the pulsar is turned off. As the nebular emission is very
inhomogeneous, our ability to effectively subtract the nebular background
signal is crucial.
No spectral lines intrinsic to the pulsar are detected. The main-pulse and
the inter-pulse behave as power laws, both with the same de-reddened index
Alpha = +0.2 +- 0.1. This value was obtained by subtracting the nebular
spectrum at the exact position of the pulsar. The underlying nebula is redder,
Alpha = -0.4 +- 0.1. Its emission lines are split into approaching (sim. -1200
km/s) and receding (sim. +600 km/s) components. The strength of emission line
components and the flux in nebular continuum vary on arcsec scale. The nebular
line and continuum intensities along the N-S slit are given.Comment: Accepted for publication in the Astrophysical Journal. 10 pages, 3
Tables, 4 Figure
Pipeline Reduction of Binary Light Curves from Large-Scale Surveys
One of the most important changes in observational astronomy of the 21st
Century is a rapid shift from classical object-by-object observations to
extensive automatic surveys. As CCD detectors are getting better and their
prices are getting lower, more and more small and medium-size observatories are
refocusing their attention to detection of stellar variability through
systematic sky-scanning missions. This trend is aditionally powered by the
success of pioneering surveys such as ASAS, DENIS, OGLE, TASS, their space
counterpart Hipparcos and others. Such surveys produce massive amounts of data
and it is not at all clear how these data are to be reduced and analysed. This
is especially striking in the eclipsing binary (EB) field, where most
frequently used tools are optimized for object-by-object analysis. A clear need
for thorough, reliable and fully automated approaches to modeling and analysis
of EB data is thus obvious. This task is very difficult because of limited data
quality, non-uniform phase coverage and solution degeneracy. This paper reviews
recent advancements in putting together semi-automatic and fully automatic
pipelines for EB data processing. Automatic procedures have already been used
to process Hipparcos data, LMC/SMC observations, OGLE and ASAS catalogs etc. We
discuss the advantages and shortcomings of these procedures.Comment: 14 pages, 8 figures, S240 IAU symposium proceeding
The GALAH survey: New diffuse interstellar bands found in residuals of 872,000 stellar spectra
We use more than 872,000 mid-to-high resolution (R 20,000) spectra of
stars from the GALAH survey to discern the spectra of diffuse interstellar
bands (DIBs). We use four windows with the wavelength range from 4718 to 4903,
5649 to 5873, 6481 to 6739, and 7590 to 7890 \AA, giving a total coverage of
967 \AA. We produce 400,000 spectra of interstellar medium (ISM)
absorption features and correct them for radial velocities of the DIB clouds.
Ultimately, we combine the 33,115 best ISM spectra into six reddening bins with
a range of . A total
of 183 absorption features in these spectra qualify as DIBs, their fitted model
parameters are summarized in a detailed catalogue. From these, 64 are not
reported in the literature, among these 17 are certain, 14 are probable and 33
are possible. We find that the broad DIBs can be fitted with a multitude of
narrower DIBs. Finally, we create a synthetic DIB spectrum at unit reddening
which should allow us to narrow down the possible carriers of DIBs and explore
the composition of the ISM and ultimately better model dust and star formation
as well as to correct Galactic and extragalactic observations. The majority of
certain DIBs show a significant excess of equivalent width when compared to
reddening. We explain this with observed lines of sight penetrating more
uniform DIB clouds compared to clumpy dust clouds.Comment: 28 pages, 15 figures, 11 tables, accepted for publication in MNRA
- …