20 research outputs found
A Fast Algorithm for Cosmic Rays Removal from Single Images
We present a method for detecting cosmic rays in single images. The algorithm
is based on simple analysis of the histogram of the image data and does not use
any modeling of the picture of the object. It does not require a good signal to
noise ratio in the image data. Identification of multiple-pixel cosmic-ray hits
is realized by running the procedure for detection and replacement iteratively.
The tests performed by us, show that the method is very effective, when applied
to the images with the spectroscopic data. It is also very fast in comparison
with other single image algorithms found in astronomical data processing
packages. Practical implementation and examples of application are presented.Comment: 12 pages, 5 figures, uses aastex.cl
CCD Photometry of Faint Variable Stars in the Globular Cluster NGC 6752
We present the results of a photometric survey for variable stars in the
field of the nearby globular cluster NGC 6752. The cluster was monitored in
1996 and 1997 for a total of 54 hours with 3 different CCD cameras mounted on
the 1.0-m Swope telescope. Eleven new variables were identified: 3 SX Phe
stars, 7 contact binaries and 1 candidate detached eclipsing binary. All 3 SX
Phe variables are likely members of the cluster while only 1 out of the 7
contact binaries is a potential cluster member. As a by-product of our survey
we obtained UBV photometry for a large sample of stars in the cluster field.
Two stars with U-B \approx -1.0 and V=19.3 and V=20.6 were identified. They lie
along the extended horizontal branch of the cluster, and are likely to be faint
sdB stars from NGC 6752.Comment: 18 pages, LaTex, 9 figures (Fig. 1 not available), accepted for
publication in the Astronomical Journa
The dust origin of the Broad Line Region and the model consequences for AGN unification scheme
We propose a very simple physical mechanism responsible for the formation of
the Low Ionization Line part of the Broad Line Region in Active Galactic
Nuclei. It explains the scaling of the Broad Line Region size with the
monochromatic luminosity, including the exact slope and the proportionality
constant, seen in the reverberation studies of nearby sources. The scaling is
independent from the mass and accretion rate of an active nucleus. The
mechanism predicts the formation of a dust-driven wind in the disk region where
the local effective temperature of a non-illuminated accretion disk drops below
1000 K and allows for dust formation. We explore now the predictive power of
the model with the aim to differentiate between this model and the previously
proposed mechanisms of the formation of the Broad Line Region. We discuss the
expected departures from the universal scaling at long wavelength, and the role
of the inclination angle of the accretion disk in the source. We compare the
expected line profiles with Mg II line profiles in the quasars observed by us
with the SALT telescope. We also discuss the tests based on the presence or
absence of the broad emission lines in low luminosity active galaxies. Finally,
we discuss the future tests of the model to be done with expected ground-based
observations and satellite missions.Comment: Based the talk presented during the COSPAR 2014 meeting, Advances in
Space Research (in press
Validating post-AGB candidates in the LMC and SMC using SALT spectra
We selected a sample of post-AGB candidates in the Magellanic Clouds on the
basis of their near- and mid-infrared colour characteristics. Fifteen of the
most optically bright post-AGB candidates were observed with the South African
Large Telescope in order to determine their stellar parameters and thus to
validate or discriminate their nature as post-AGB objects in the Magellanic
Clouds. The spectral types of absorption-line objects were estimated according
to the MK classification, and effective temperatures were obtained by means of
stellar atmosphere modelling. Emission-line objects were classified on the
basis of the fluxes of the emission lines and the presence of the continuum.
Out of 15 observed objects, only 4 appear to be genuine post-AGB stars (27\%).
In the SMC, 1 out of 4 is post-AGB, and in the LMC, 3 out 11 are post-AGB
objects. Thus, we can conclude that the selected region in the colour-colour
diagram, while selecting the genuine post-AGB objects, overlaps severely with
other types of objects, in particular young stellar objects and planetary
nebulae. Additional classification criteria are required to distinguish between
post-AGB stars and other types of objects. In particular, photometry at far-IR
wavelengths would greatly assist in distinguishing young stellar objects from
evolved ones. On the other hand, we showed that the low-resolution optical
spectra appear to be sufficient to determine whether the candidates are
post-AGB objects.Comment: 19 pages, 19 figures, A&A in pres
SN 2005bf: A possible transition event between type Ib/c supernovae and gamma-ray bursts
We present u′g′r′i′BV photometry and optical spectroscopy of the Type Ib/Ic SN 2005bf covering the first ∼100 days following discovery. The u′g′BV light curves displayed an unprecedented morphology among Type Ib/Ic supernovae, with an initial maximum some 2 weeks after discovery and a second, main maximum about 25 days after that. The bolometric light curve indicates that SN 2005bf was a remarkably luminous event, radiating at least 6.3 × 1042 ergs s -1 at maximum light and a total of 2.1 × 1049 ergs during the first 75 days after the explosion. Spectroscopically, SN 2005bf underwent a unique transformation from a Type Ic-like event at early times to a typical Type Ib supernova at later phases. The initial maximum in u′g′BV was accompanied by the presence in the spectrum of high-velocity (>14,000 km s-1) absorption lines of Fe II, Ca II, and H I. The photospheric velocity derived from spectra at early epochs was below 10,000 km s-1, which is unusually low compared with ordinary Type Ib supernovae. We describe one-dimensional computer simulations that attempt to account for these remarkable properties. The most favored model is that of a very energetic (2 × 1051 ergs), asymmetric explosion of a massive (8.3 M⊙) Wolf-Rayet WN star that had lost most of its hydrogen envelope. We speculate that an unobserved relativistic jet was launched producing a two-component explosion consisting of (1) a polar explosion containing a small fraction of the total mass and moving at high velocity and (2) the explosion of the rest of the star. At first, only the polar explosion is observed, producing the initial maximum and the high-velocity absorption-line spectrum resembling a Type Ic event. At late times, this fast-moving component becomes optically thin, revealing the more slowly moving explosion of the rest of the star and transforming the observed spectrum to that of a typical Type Ib supernova. If this scenario is correct, then SN 2005bf is the best example to date of a transition object between normal Type Ib/Ic supernovae and γ-ray bursts.Facultad de Ciencias Astronómicas y Geofísica
Radial Velocity Studies of Close Binary Stars. IX
Radial-velocity measurements and sine-curve fits to the orbital velocity
variations are presented for the eighth set of ten close binary systems: AB
And, V402 Aur, V445 Cep, V2082 Cyg, BX Dra, V918 Her, V502 Oph, V1363 Ori, KP
Peg, V335 Peg. Half of the systems (V445 Cep, V2082 Cyg, V918 Her, V1363 Ori,
V335 Peg) were discovered photometrically by the Hipparcos mission and all
systems are double-lined (SB2) contact binaries. The broadening function method
permitted improvement of the orbital elements for AB And and V502 Oph. The
other systems have been observed for radial velocity variations for the first
time; in this group are five bright (V<7.5) binaries: V445 Cep, V2082 Cyg, V918
Her, KP Peg and V335 Peg. Several of the studied systems are prime candidates
for combined light and radial-velocity synthesis solutions.Comment: 17+ pages, 2 tables, 4 figure
Time-delay measurement of MgII broad line response for the highly-accreting quasar HE 0413-4031: Implications for the MgII-based radius-luminosity relation
We present the monitoring of the AGN continuum and MgII broad line emission
for the quasar HE 0413-4031 () based on the six-year monitoring by the
South African Large Telescope (SALT). We managed to estimate a time-delay of
days in the rest frame of the source using seven
different methods: interpolated cross-correlation function (ICCF), discrete
correlation function (DCF), -transformed DCF, JAVELIN, two estimators of
data regularity (Von Neumann, Bartels), and method. This time-delay is
below the value expected from the standard radius-luminosity relation. However,
based on the monochromatic luminosity of the source and the SED modelling, we
interpret this departure as the shortening of the time-delay due to the higher
accretion rate of the source, with the inferred Eddington ratio of .
The MgII line luminosity of HE 0413-4031 responds to the continuum variability
as , which is consistent with
the light-travel distance of the location of MgII emission at . Using the data of 10 other quasars, we confirm the
radius-luminosity relation for broad MgII line, which was previously determined
for broad H line for lower-redshift sources. In addition, we detect a
general departure of higher-accreting quasars from this relation in analogy to
H sample. After the accretion-rate correction of the light-travel
distance, the MgII-based radius-luminosity relation has a small scatter of only
dex.Comment: 39 pages (23 pages - Main text, 16 pages - Appendix), 21 figures, 14
tables; accepted for publication in the Astrophysical Journa
SN 2005bf: A Possible Transition Event Between Type Ib/c Supernovae and Gamma Ray Bursts
We present u'g'r'i'BV photometry and optical spectroscopy of the Type Ib/Ic
SN 2005bf covering the first ~100 days following discovery. The u'g'BV light
curves displayed a double-peaked morphology, which is among Type Ib/Ic
supernovae. The bolometric light curve indicates that SN 2005bf was a
remarkably luminous event. Spectroscopically, SN 2005bf underwent a unique
transformation from a Type Ic-like event at early times to a typical Type Ib
supernova at later phases. The initial maximum in u'g'BV was accompanied by the
presence in the spectrum of high velocity absorption lines of Fe II, Ca II, and
H I. The photospheric velocity derived from spectra at early epochs was
unusually low compared with ordinary Type Ib supernovae. We describe
one-dimensional computer simulations which attempt to account for these
remarkable properties. The most favored model is that of a very energetic (2 x
10^{51} erg), asymmetric explosion of a massive (8.3 M_sun) Wolf-Rayet WN star
that had lost most of its hydrogen envelope. We speculate that an unobserved
relativistic jet was launched producing a two-component explosion consisting of
1) a polar explosion containing a small fraction of the total mass and moving
at high velocity, and 2) the explosion of the rest of the star. At first, only
the polar explosion is observed, producing the initial maximum and the high
velocity absorption-line spectrum resembling a Type Ic event. At late times,
this fast-moving component becomes optically-thin, revealing the slower-moving
explosion of the rest of the star and transforming the observed spectrum to
that of a typical Type Ib supernova. If this scenario is correct, then SN
2005bf is the best example to date of a transition object between normal Type
Ib/Ic supernovae and gamma ray bursts.Comment: Accepted ApJ on 15 December 2005, 37 pages, 11 figures; minor changes
after refereeing proces
Time delay measurement of Mg II line in CTS C30.10 with SALT
We report 6 yr monitoring of a distant bright quasar CTS C30.10 (z = 0.90052)
with the Southern African Large Telescope (SALT). We measured the rest-frame
time-lag of days between the continuum variations and the response
of the Mg II emission line, using the Javelin approach. More conservative
approach, based on five different methods, imply the time delay of
days. This time delay, combined with other available
measurements of Mg II line delay, mostly for lower redshift sources, shows that
the Mg II line reverberation implies a radius-luminosity relation very similar
to the one based on a more frequently studied H line.Comment: submitted to ApJ; comments welcom
Radial Velocity Studies of Close Binary Stars. XI
Radial-velocity measurements and sine-curve fits to the orbital radial
velocity variations are presented for ten close binary systems: DU Boo, ET Boo,
TX Cnc, V1073 Cyg, HL Dra, AK Her, VW LMi, V566 Oph, TV UMi and AG Vir. By this
contribution, the DDO program has reached the point of 100 published radial
velocity orbits. The radial velocities have been determined using an improved
fitting technique which uses rotational profiles to approximate individual
peaks in broadening functions.
Three systems, ET Boo, VW LMi and TV UMi, were found to be quadruple while AG
Vir appears to be a spectroscopic triple. ET Boo, a member of a close visual
binary with years, was previously known to be a multiple
system, but we show that the second component is actually a close,
non-eclipsing binary. The new observations enabled us to determine the
spectroscopic orbits of the companion, non-eclipsing pairs in ET Boo and VW
LMi. The particularly interesting case is VW LMi, where the period of the
mutual revolution of the two spectroscopic binaries is only 355 days.
While most of the studied eclipsing pairs are contact binaries, ET Boo is
composed of two double-lined detached binaries and HL Dra is single-lined
detached or semi-detached system. Five systems of this group were observed
spectroscopically before: TX Cnc, V1073 Cyg, AK Her (as a single-lined binary),
V566 Oph, AG Vir, but our new data are of much higher quality than the previous
studies.Comment: Accepted by AJ, August 2006, 10 figures, 3 table