1,454 research outputs found
Circumstellar Disks revealed by / Flux Variation Gradients
The variability of young stellar objects (YSO) changes their brightness and
color preventing a proper classification in traditional color-color and color
magnitude diagrams. We have explored the feasibility of the flux variation
gradient (FVG) method for YSOs, using and band monitoring data of the
star forming region RCW\,38 obtained at the University Observatory Bochum in
Chile. Simultaneous multi-epoch flux measurements follow a linear relation
for almost all YSOs with large variability
amplitude. The slope gives the mean color temperature of
the varying component. Because is hotter than the dust sublimation
temperature, we have tentatively assigned it to stellar variations. If the
gradient does not meet the origin of the flux-flux diagram, an additional non-
or less-varying component may be required. If the variability amplitude is
larger at the shorter wavelength, e.g. , this component is cooler
than the star (e.g. a circumstellar disk); vice versa, if , the
component is hotter like a scattering halo or even a companion star. We here
present examples of two YSOs, where the FVG implies the presence of a
circumstellar disk; this finding is consistent with additional data at and
. One YSO shows a clear -band excess in the color-color diagram,
while the significance of a -excess in the other YSO depends on the
measurement epoch. Disentangling the contributions of star and disk it turns
out that the two YSOs have huge variability amplitudes (\,mag). The
FVG analysis is a powerful complementary tool to analyze the varying
components of YSOs and worth further exploration of monitoring data at other
wavelengths.Comment: 5 pages, 5 figures, accepted for publication in Astronomy and
Astrophysic
Photometric reverberation mapping of 3C120
We present the results of a five month monitoring campaign of the local
active galactic nuclei (AGN) 3C120. Observations with a median sampling of two
days were conducted with the robotic 15cm telescope VYSOS-6 located near Cerro
Armazones in Chile. Broad band (B,V) and narrow band (NB) filters were used in
order to measure fluxes of the AGN and the H_beta broad line region (BLR)
emission line. The NB flux is constituted by about 50% continuum and 50% H_beta
emission line. To disentangle line and continuum flux, a synthetic H_beta light
curve was created by subtracting a scaled V-band light curve from the NB light
curve. Here we show that the H_beta emission line responds to continuum
variations with a rest frame lag of 23.6 +/- 1.69 days. We estimate a virial
mass of the central black hole M_BH = 57 +/- 27 * 10^6 solar masses, by
combining the obtained lag with the velocity dispersion of a single
contemporaneous spectrum. Using the flux variation gradient (FVG) method, we
determined the host galaxy subtracted rest frame 5100A luminosity at the time
of our monitoring campaign with an uncertainty of 10% (L_AGN = 6.94 +/- 0.71*
10^43 ergs^-1). Compared with recent spectroscopic reverberation results, 3C120
shifts in the R_BLR - L_AGN diagram remarkably close to the theoretically
expected relation of R-L^0.5. Our results demonstrate the performance of
photometric AGN reverberation mapping, in particular for efficiently
determining the BLR size and the AGN luminosityComment: 11 pages, 11 figures, Published in Astronomy and Astrophysic
Eclipsing high-mass binaries I. Light curves and system parameters for CPD-518946, PISMIS24-1 and HD319702
We present first results of a comprehensive photometric O-star survey
performed with a robotic twin refractor at the Universit\"atssternwarte Bochum
located near Cerro Armazones in Chile. For three high-mass stars, namely
Pismis24-1, CPD-518946 and HD319702, we determined the period through the
Lafler-Kinman algorithm and model the light curves within the framework of the
Roche geometry. For Pismis24-1, a previously known eclipsing binary, we provide
first light curves and determined a photometric period of 2.36 days together
with an orbital inclination of 61.8 degrees. The best-fitting model solution to
the light curves suggest a detached configuration. With a primary temperature
of T1 = 42520K we obtain the temperature of the secondary component as T2 =
41500K. CPD-518946 is another known eclipsing binary for which we present a
revised photometric period of 1.96 days with an orbital inclination of 58.4
degrees. The system has likely a semi-detached configuration and a mass ratio q
= M1/M2 = 2.8. If we adopt a primary temperature of T1 = 34550K we obtain T2 =
21500K for the secondary component. HD319702 is a newly discovered eclipsing
binary member of the young open cluster NGC6334. The system shows well-defined
eclipses favouring a detached configuration with a period of 2.0 days and an
orbital inclination of 67.5 degrees. Combining our photometric result with the
primary spectral type O8 III(f) (T1 = 34000K) we derive a temperature of T2 =
25200K for the secondary component.Comment: 7 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
Modelling photometric reverberation data -- a disk-like broad-line region and a potentially larger black hole mass for 3C120
We consider photometric reverberation mapping, where the nuclear continuum
variations are monitored via a broad-band filter and the echo of emission line
clouds of the broad line region (BLR) is measured with a suitable narrow-band
(NB) filter. We investigate how an incomplete emission-line coverage by the NB
filter influences the BLR size determination. This includes two basic cases: 1)
a symmetric cut of the blue and red part of the line wings, and 2) the filter
positioned asymmetrically to the line centre so that essentially a complete
half of the emission line is contained in the NB filter. Under the assumption
that the BLR size is dominated by circular Keplerian orbits, we find that
symmetric cutting of line wings may lead to overestimating the BLR size by less
than 5%. The case of asymmetric half-line coverage, similar as for our data of
the Seyfert 1 galaxy 3C120, yields the BLR size with a bias of less than 1%.
Our results suggest that any BLR size bias due to narrow-band line cut in
photometric reverberation mapping is small and in most cases negligible. We
used well sampled photometric reverberation mapping light curves with sharp
variation features in both the continuum and the Hbeta light curves to
determine the geometry type of the Hbeta BLR for 3C120. Modelling of the light
curve, under the assumption that the BLR is essentially virialised, argues
against a spherical geometry and favours a nearly face-on disk-like geometry
with inclination i = 10 +/- 4 deg and extension from 22 to 28 light days. The
low inclination may lead to a larger black hole mass than the derived when
using the average geometry scaling factor f=5.5. We discuss deviations of
Seyfert 1 galaxies from the M_BH - sigma relation.Comment: 9 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
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