171 research outputs found
The Distances of the Galactic Novae
Utilising the unique location of red clump giants on colour-magnitude
diagrams obtained from various near-IR surveys, we derived specific
reddening-distance relations towards 119 Galactic novae for which independent
reddening measurements are available. Using the derived distance-extinction
relation and the independent measurements of reddening we calculated the most
likely distances for each system. We present the details of our distance
measurement technique and the results of this analysis, which yielded the
distances of 73 Galactic novae and allowed us to set lower limits on the
distances of 46 systems. We also present the reddening-distance relations
derived for each nova, which may be useful to analyze the different Galactic
components present in the line of sight.Comment: Published in MNRAS (24 pages, 12 figures, 4 tables), Minor typo
correction. For the catalogue which has all reddening-distance relations, see
http://highenergyastro.istanbul.edu.tr/novae_cat/index.php,
2016MNRAS.461.1177
Population types of cataclysmic variables in the solar neighborhood
The Galactic orbital parameters of 159 cataclysmic variables in the Solar neighbourhood are calculated, for the first time, to determine their population types using published kinematical parameters. Population analysis shows that about 6 per cent of cataclysmic variables in the sample are members of the thi
ck disc component of the Galaxy. This value is consistent with the fraction obt
ained from star count analysis. The rest of the systems in the sample are found to be in the thin disc component of the Galaxy. Our analysis revealed no halo CVs in the Solar vicinity. About 60 per cent of the thick disc CVs have orbital periods be low the orbital period gap. This result is roughly consistent with the predictions of population synthesis models developed for cataclysmic variables. A kinematical age of 13 Gyr is obtained using total space velocity dispersion of the most probable thick disc CVs which is consistent with the age of thick disc component of the Galaxy
A New Catalogue of Galactic Novae: Investigation of the MMRD relation & Spatial Distribution
In this study, a new Galactic novae catalogue is introduced collecting
important parameters of these sources such as their light curve parameters,
classifications, full width half maximum (FWHM) of H line, distances
and interstellar reddening estimates. The catalogue is also published on a
website with a search option via a SQL query and an online tool to re-calculate
the distance/reddening of a nova from the derived reddening-distance relations.
Using the novae in the catalogue, the existence of a maximum magnitude-rate of
decline (MMRD) relation in the Galaxy is investigated. Although an MMRD
relation was obtained, a significant scattering in the resulting MMRD
distribution still exists. We suggest that the MMRD relation likely depends on
other parameters in addition to the decline time, as FWHM H, the light
curve shapes. Using two different samples depending on the distances in the
catalogue and from the derived MMRD relation, the spatial distributions of
Galactic novae as a function of their spectral and speed classes were studied.
The investigation on the Galactic model parameters implies that best estimates
for the local outburst density are 3.6 and 4.2 pc
yr with a scale height of 148 and 175 pc, while the space density
changes in the range of pc. The local
outburst density and scale height obtained in this study infer that the disk
nova rate in the Galaxy is in the range of to yr with
an average estimate yr.Comment: 24 pages, 9 figures, 6 tables; Accepted for publication in MNRAS on
13 Feb 201
The orbital period of Nova V2540 Ophiuchi (2002)
We present the results of 26 nights of CCD photometry of the nova V2540 Oph
(2002) from 2003 and 2004. We find a period of 0.284781 +/- 0.000006 d (6.8347
+/- 0.0001 h) in the data. Since this period was present in the light curves
taken in both years, with no apparent change in its value or amplitude, we
interpret it as the orbital period of the nova binary system. The mass-period
relation for cataclysmic variables yields a secondary mass of about 0.75 +/-
0.04 Msun. From maximum magnitude - rate of decline relation, we estimate a
maximum absolute visual magnitude of M(V)=-6.2 +/- 0.4 mag. This value leads to
an uncorrected distance modulus of (m-M) = 14.7 +/- 0.7. By using the
interstellar reddening for the location of V2540 Oph, we find a rough estimate
for the distance of 5.2 +/- 0.8 kpc. We propose that V2540 Oph is either: 1) a
high inclination cataclysmic variable showing a reflection effect of the
secondary star, or having a spiral structure in the accretion disc, 2) a high
inclination intermediate polar system, or less likely 3) a polar.Comment: 8 pages, 7 figures, accepted by PAS
Astronomical Site Selection for Turkey Using GIS Techniques
A site selection of potential observatory locations in Turkey have been
carried out by using Multi-Criteria Decision Analysis (MCDA) coupled with
Geographical Information Systems (GIS) and satellite imagery which in turn
reduced cost and time and increased the accuracy of the final outcome. The
layers of cloud cover, digital elevation model, artificial lights, precipitable
water vapor, aerosol optical thickness and wind speed were studied in the GIS
system. In conclusion of MCDA, the most suitable regions were found to be
located in a strip crossing from southwest to northeast including also a
diverted region in southeast of Turkey. These regions are thus our prime
candidate locations for future on-site testing. In addition to this major
outcome, this study has also been applied to locations of major observatories
sites. Since no goal is set for \textit{the best}, the results of this study is
limited with a list of positions. Therefore, the list has to be further
confirmed with on-site tests. A national funding has been awarded to produce a
prototype of an on-site test unit (to measure both astronomical and
meteorological parameters) which might be used in this list of locations.Comment: 17 pages, 10 figures, accepted by Experimental Astronom
First day-time seeing observations at the TUBITAK National Observatory in Turkey
Despite the fact that selecting good solar observatory sites is an important matter, day-time seeing quality of observatory sites in Turkey has not been previously recorded. Therefore, we built a Solar Differential Image Motion Monitor (S-DIMM) for day-time seeing observations at the TUBITAK National Observatory (TUG) in Turkey which is being tested as a likely site for a future large aperture solar telescope. In this study, we describe the design of TUG S-DIMM instrument and a reduction procedure for its data. First results obtained at 7 m above ground show that the day-time Fried parameters at the TUG site are comparable with those of some solar observatory sites. The best seeing conditions at the TUG site occur between October and December with a median Fried parameter of 6.95 cm in the first three hours of the day. The median Fried parameter calculated from all observations made during our observation period is 4.48 cm. Our observations also reveal that the best day-time Fried parameters are obtained for wind speeds higher than 3 m/s
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