6 research outputs found
Near-Infrared Colours of Active Galactic Nuclei
We propose near-infrared colour selection criteria to extract Active Galactic
Nuclei (AGNs) using the near-infrared Colour-Colour Diagram (CCD) and predict
near-infrared colour evolution with respect to redshift. First, we
cross-identify two AGN catalogues with the 2MASS Point Source Catalogue, and
confirm both the loci of quasars/AGNs in the near-infrared CCD and
redshift-colour relations. In the CCD, the loci of over 70 - 80% of AGNs can be
distinguished from the stellar locus. To examine the colours of quasars, we
simulate near-infrared colours using Hyperz code. Assuming a realistic quasar
SED, we derive simulated near-infrared colours of quasars with redshift (up to
z ~ 11). The simulated colours can reproduce not only the redshift-colour
relations but also the loci of quasars/AGNs in the near-infrared CCD. We
finally discuss the possibility of contamination by other types of objects. We
compare the locus of AGNs with the other four types of objects (namely,
microquasars, CVs, LMXBs, and MYSOs) which have a radiation mechanism similar
to that of AGNs. In the near-infrared CCD, each type of object is located at a
position similar to the stellar locus. Accordingly, it is highly probable that
the four types of objects can be distinguished on the basis of the locus in a
near-infrared CCD. We additionally consider contamination by distant normal
galaxies. The near-infrared colours of several types of galaxies are also
simulated using the Hyperz code. Although galaxies with z ~ 1 have
near-infrared colours similar to those of AGNs, these galaxies are unlikely to
be detected because they are very faint. In other words, few galaxies should
contaminate the locus of AGNs in the near-infrared CCD. Consequently, we can
extract reliable AGN candidates on the basis of the near-infrared CCD.Comment: 7 pages, 6 figures, Accepted for publication in A&
Mass ratio estimates for overcontact binaries using the derivatives of light curves
The photometric mass ratios of eclipsing binaries are usually estimated by
light-curve modeling with an iterative method. We propose a new method for
estimating the photometric mass ratio of an overcontact binary using the
derivatives of a light curve, which provides a reasonable uncertainty value.
The method mainly requires only the time interval value between two local
extrema found in the third derivative of a light curve, with no need of an
iterative procedure. We applied the method to a sample of real overcontact
binary data and compared the estimated mass ratios with their spectroscopically
determined values. The comparison showed that our estimated mass ratios for
67% of the samples agreed with their spectroscopic mass ratios within
the estimated uncertainties, and the errors for 95% of them are within . Our method should be useful for estimating mass ratios for numerous
overcontact eclipsing binaries found with existing and future surveys, as well
as for the light-curve analysis of each system.Comment: 7 pages, 5 figures, accepted for publication in Ap
Properties of Large-Amplitude Variable Stars Detected With Two Micron All Sky Survey Public Images
We present a catalogue of variable stars in the near-infrared wavelength
detected with overlapping regions of the 2MASS public images, and discuss their
properties. The investigated region is in the direction of the Galactic center
(-30 < l < 20, |b| < 20), which covers the entire bulge. We have detected 136
variable stars, of which 6 are already-known and 118 are distributed in |b| < 5
region. Additionally, 84 variable stars have optical counterparts in DSS
images. The three diagrams (colour-magnitude, light variance and colour-colour
diagrams) indicate that most of the detected variable stars should be
largeamplitude and long-period variables such as Mira variables or OH/IR stars.
The number density distribution of the detected variable stars implies that
they trace the bar structure of the Galactic bulge.Comment: Published in AJ, 34 pages, 12 figure