Circumstellar Disks revealed by HH/KK 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 $H$ and $K$ 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 $F_{H}=\alpha + \beta \cdot F_{K}$ for almost all YSOs with large variability amplitude. The slope $\beta$ gives the mean $HK$ color temperature $T_{var}$ of the varying component. Because $T_{var}$ 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. $\alpha < 0$, this component is cooler than the star (e.g. a circumstellar disk); vice versa, if $\alpha > 0$, the component is hotter like a scattering halo or even a companion star. We here present examples of two YSOs, where the $HK$ FVG implies the presence of a circumstellar disk; this finding is consistent with additional data at $J$ and $L$. One YSO shows a clear $K$-band excess in the $JHK$ color-color diagram, while the significance of a $K$-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 ($\sim 3-5$\,mag). The $HK$ 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

Dust reverberation-mapping of the Seyfert 1 galaxy WPVS48

Using robotic telescopes of the Universitatssternwarte Bochum near Cerro Armazones in Chile, we monitored the z=0.0377 Seyfert 1 galaxy WPVS48 (2MASX J09594263-3112581) in the optical (B and R) and near-infrared (NIR, J and Ks) with a cadence of two days. The light curves show unprecedented variability details. The NIR variation features of WPVS48 are consistent with the corresponding optical variations, but the features appear sharper in the NIR than in the optical, suggesting that the optical photons undergo multiple scatterings. The J and Ks emission, tracing the hot (1600 K) dust echo, lags the B and R variations by on average 64 +/- 4 days and 71 +/- 5 days, respectively (restframe). WPVS48 lies on the known tau-M_V relationship. However, the observed lag is about three times shorter than expected from the dust sublimation radius r_sub inferred from the optical-UV luminosity, and explanations for this common discrepancy are searched for. The sharp NIR echos argue for a face-on torus geometry and allow us to put forward two potential scenarios: 1) as previously proposed, in the equatorial plane of the accretion disk the inner region of the torus is flattened and may come closer to the accretion disk. 2) The dust torus with inner radius r_sub is geometrically and optically thick, so that the observer only sees the facing rim of the torus wall, which lies closer to the observer than the torus equatorial plane and therefore leads to an observed foreshortened lag. Both scenarios are able to explain the factor three discrepancy between tau and r_sub. Longer-wavelength dust reverberation data might enable one to distinguish between the scenarios.Comment: 4 pages, 6 figures, Published in Astronomy and Astrophysic

The broad-line region and dust torus size of the Seyfert 1 galaxy PGC50427

We present the results of a three years monitoring campaigns of the $z = 0.024$ type-1 active galactic nucleus (AGN) PGC50427. Through the use of Photometric Reverberation Mapping with broad and narrow band filters, we determine the size of the broad-line emitting region by measuring the time delay between the variability of the continuum and the H$\alpha$ emission line. The H$\alpha$ emission line responds to blue continuum variations with an average rest frame lag of $19.0 \pm 1.23$ days. Using single epoch spectroscopy we determined a broad-line H$\alpha$ velocity width of 1020 km s$^{-1}$ and in combination with the rest frame lag and adoption a geometric scaling factor $f = 5.5$, we calculate a black hole mass of $M_{BH} \sim 17 \times 10^{6} M_{\odot}$. Using the flux variation gradient method, we separate the host galaxy contribution from that of the AGN to calculate the rest frame 5100\AA~ luminosity at the time of our monitoring campaign. The rest frame lag and the host-subtracted luminosity permit us to derive the position of PGC50427 in the BLR size -- AGN luminosity diagram, which is remarkably close to the theoretically expected relation of $R \propto L^{0.5}$. The simultaneous optical and NIR ($J$ and $K_{s}$) observations allow us to determine the size of the dust torus through the use of dust reverberation mapping method. We find that the hot dust emission ($\sim 1800K$) lags the optical variations with an average rest frame lag of $46.2 \pm 2.60$ days. The dust reverberation radius and the nuclear NIR luminosity permit us to derive the position of PGC50427 on the known $\tau - M{V}$ diagram. The simultaneus observations for the broad-line region and dust thermal emission demonstrate that the innermost dust torus is located outside the BLR in PGC50427, supporting the unified scheme for AGNs. (Abstract shortened, see the manuscript.)Comment: 11 pages, 23 figures, accepted for publication in Astronomy and Astrophysic

Size and disk-like shape of the broad-line region of ESO399-IG20

We present photometric reverberation mapping of the narrow-line Seyfert 1 galaxy ESO399-IG20 performed with the robotic 15 cm telescope VYSOS-6 at the Cerro Armazones Observatory. Through the combination of broad- and narrow-band filters we determine the size of the broad-line emitting region (BLR) by measuring the time delay between the variability of the continuum and the H_alpha emission line. We use the flux variation gradient method to separate the host galaxy contribution from that of the active galactic nucleus (AGN), and to calculate the 5100A luminosity L_AGN of the AGN. Both measurements permit us to derive the position of ESO399-IG20 in the BLR size -- AGN luminosity R_BLR-L_AGN^0.5 diagram. We infer the basic geometry of the BLR through modelling of the light curves. The pronounced sharp variability patterns in both the continuum and the emission line light curves allow us to reject a spherical BLR geometry. The light curves are best fitted by a disk-like BLR seen nearly face-on with an inclination angle of 6+/-3 degrees and with an extension from 16 to 20 light days.Comment: 9 pages, 13 figures, Published in Astronomy and Astrophysic