ABSTRACT
We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC 3516 carried out in 2018 to 2020 covering the wavelength range from the X-ray to the ...optical. The facilities included the telescopes of the CMO SAI MSU, the 2.3-m WIRO telescope, and the XRT and UVOT of Swift. We found that NGC 3516 brightened to a high state and could be classified as Sy1.5 during the late spring of 2020. We have measured time delays in the responses of the Balmer and He ii λ4686 lines to continuum variations. In the case of the best-characterized broad H β line, the delay to continuum variability is about 17 d in the blue wing and is clearly shorter, 9 d, in the red, which is suggestive of inflow. As the broad lines strengthened, the blue side came to dominate the Balmer lines, resulting in very asymmetric profiles with blueshifted peaks during this high state. During the outburst the X-ray flux reached its maximum on 2020 April 1 and it was the highest value ever observed for NGC 3516 by the Swift observatory. The X-ray hard photon index became softer, ∼1.8 in the maximum on 2020 April 21 compared to the mean ∼0.7 during earlier epochs before 2020. We have found that the UV and optical variations correlated well (with a small time delay of 1–2 d) with the X-ray until the beginning of 2020 April, but later, until the end of 2020 June, these variations were not correlated. We suggest that this fact may be a consequence of partial obscuration by Compton-thick clouds crossing the line of sight.
ABSTRACT
We report the discovery of a nearby massive white dwarf with He–H atmosphere. The white dwarf is located at a distance of 74.5 ± 0.9 pc. Its radius, mass, effective temperature, H/He ratio, ...and age are R = 2500 ± 100 km, M = 1.33 ± 0.01 $\rm M_{\odot }$, Teff = 31 200 ± 1200 K, H/He ∼ 0.1, and 330 ± 40 Myr, respectively. The observed spectrum is redshifted by Vr = +240 ± 15 km s−1, which is mostly attributed to the gravitational redshift. The white dwarf shows a regular stable photometric variability with amplitude Δg ≈ 0.06m and period P = 353.456 s suggesting rapid rotation. This massive, hot, and rapidly rotating white dwarf is likely to originate from the merging of close binary white dwarf system that avoided explosion in a thermonuclear Type Ia supernova.
ABSTRACT
We present the results of multicolour UBVRCICJHK photometry, spectroscopic analysis and spectral energy distribution (SED) modelling for the post-AGB candidate IRAS 02143+5852. We detected ...Cepheid-like light variations with the full peak-to-peak amplitude ΔV ∼ 0.9 mag and the pulsation period of about 24.9 d. The phased light curves appeared typical for the W Vir Cepheids. The period–luminosity relation for the Type II Cepheids yielded the luminosity logL/L⊙ ∼ 2.95. From a low-resolution spectrum, obtained at maximum brightness, the following atmospheric parameters were determined: Teff ∼ 7400 K and logg ∼ 1.38. This spectrum contains the emission lines H α, ${\rm Ba\, {\small II}}$ λ6496.9, ${\rm He\, {\small I}}$λ10830, and Pa β. Spectral monitoring performed in 2019–2021 showed a significant change in the H α profile and appearance of CH and CN molecular bands with pulsation phase. The metal lines are weak. Unlike typical W Vir variables, the star shows a strong excess of infrared radiation associated with the presence of a heavy dust envelope around the star. We modelled the SED using our photometry and archival data from different catalogues and determined the parameters of the circumstellar dust envelope. We conclude that IRAS 02143+5852 is a low-luminosity analogue of dusty RV Tau stars.
We present observations of the vdB 130 cluster vicinity in a narrow-band filter centered at a
molecular hydrogen line performed at the Caucasus Mountain Observatory of the Lomonosov Moscow State ...University. The observations reveal an H
emission shell around vdB 130, coincident with a bright infrared shell, visible in all Spitzer bands. Also, numerous H
emission features are detected around infrared Blobs E and W and in the vicinity of a protocluster located to the east of the shell, in a tail of a cometary molecular cloud. H
emission in the vicinity of the vdB 130 cluster is mostly generated in well-developed H II regions and is of fluorescent nature. In the protocluster area, isolated spots are observed, where H
emission is collisionally excited and is probably related to shocks in protostellar outflows. Obtained results are discussed in the context of possible sequential star formation in the vicinity of the vdB 130 cluster, triggered by the interaction of the expanding supershell surrounding the Cyg OB1 association with the molecular cloud and an associated molecular filament.
photometry for the carbon Mira star V CrB are presented. The infrared observations were carried out in the time interval 1989–2018, while the
,
, and
data were obtained in 2001–2014. The light and ...color curves are analyzed. The pulsation period of V CrB has been found to be
in the infrared
bands and
for the optical
band. In the
bands, apart from periodic pulsations, there are distinct sinusoidal variations in the average brightness level with a characteristic period of
days. Color–magnitude relationships have been revealed for the infrared and optical bands. The phase curves exhibit the wavelength dependence of the brightness variability amplitude. The light curves for various bands and colors are discussed. We have constructed the model of a spherically symmetric circumstellar dust envelope that allows the observed spectral energy distribution at both maximum and minimum light to be reproduced equally well (within the model assumptions) and is consistent with the observations of V CrB by differential speckle polarimetry. The model is characterized by the following parameters: the optical depth is
, the inner and outer radii of the envelope are 8 and 40 000 AU, respectively. The envelope contains spherical carbon dust grains (
by mass) and silicon carbide dust grains. Dust grains with a radius of 0.5
m account for
of the envelope mass. The remaining
of the mass is accounted for by finer dust with a grain radius of 0.1
m. Based on the observational data, we have estimated the bolometric flux from V CrB:
and
erg cm
s
at minimum and maximum light, respectively. The effective temperature of the star is
K at maximum light and
K at minimum light.
We present the results of multicolour \(UBVR_{\text{C}}I_{\text{C}}JHK\) photometry, spectroscopic analysis and spectral energy distribution (SED) modelling for the post-AGB candidate IRAS ...02143+5852. We detected Cepheid-like light variations with the full peak-to-peak amplitude \(\Delta V\sim0.9\) mag and the pulsation period of about 24.9 d. The phased light curves appeared typical for the W Vir Cepheids. The period-luminosity relation for the Type II Cepheids yielded the luminosity \(\log L/L_{\odot}\sim2.95\). From a low-resolution spectrum, obtained at maximum brightness, the following atmospheric parameters were determined: \(T_\text{eff}\sim7400\) K and \(\log g\sim1.38\). This spectrum contains the emission lines H\(\alpha\), BaII \(\lambda\)6496.9, HeI \(\lambda\)10830 and Pa\(\beta\). Spectral monitoring performed in 2019-2021 showed a significant change in the H\(\alpha\) profile and appearance of CH and CN molecular bands with pulsation phase. The metal lines are weak. Unlike typical W Vir variables, the star shows a strong excess of infrared radiation associated with the presence of a heavy dust envelope around the star. We modelled the SED using our photometry and archival data from different catalogues and determined the parameters of the circumstellar dust envelope. We conclude that IRAS~02143+5852 is a low-luminosity analogue of dusty RV Tau stars.
We present observations of the vdB 130 cluster vicinity in a narrow-band filter centered at a \(2.12\,\mu\)m molecular hydrogen line performed at the Caucasus Mountain Observatory of the Lomonosov ...Moscow State University. The observations reveal an H\(_2\) emission shell around vdB 130, coincident with a bright infrared shell, visible in all \textit{Spitzer} bands. Also, numerous H\(_{2}\) emission features are detected around infrared Blobs E and W and in the vicinity of a protocluster located to the east of the shell, in a tail of a cometary molecular cloud. H\(_2\) emission in the vicinity of the vdB~130 cluster is mostly generated in well-developed \HII\ regions and is of fluorescent nature. In the protocluster area, isolated spots are observed, where H\(_2\) emission is collisionally excited and is probably related to shocks in protostellar outflows. Obtained results are discussed in the context of possible sequential star formation in the vicinity of the vdB 130 cluster, triggered by the interaction of the expanding supershell surrounding the Cyg OB1 association with the molecular cloud and an associated molecular filament.
We report the discovery of a nearby massive white dwarf with He-H atmosphere. The white dwarf is located at a distance of \(74.5\pm0.9\) pc. Its radius, mass, effective temperature, H/He ratio and ...age are \(R=2500\pm100\) km, \(M=1.33\pm0.01\) \(\rm M_{\odot}\), \(T_{\mathrm{eff}}=31200\pm 1200\) K, \({\mathrm{H/He}}\sim0.1\) and \(330\pm40\) Myr, respectively. The observed spectrum is redshifted by \(V_{\mathrm{r}}=+240\pm15\) km s\(^{-1},\) which is mostly attributed to the gravitational redshift. The white dwarf shows a regular stable photometric variability with amplitude \(\Delta g\approx0.06^{\mathrm{m}}\) and period \(P=353.456\) s suggesting rapid rotation. This massive, hot and rapidly rotating white dwarf is likely to originate from the merging of close binary white dwarf system that avoided explosion in a thermonuclear type Ia supernova at the Carboniferous Period of the Earth history.
We present the results of photometric and spectroscopic monitoring campaigns of the changing look AGN NGC 3516 carried out in 2018 to 2020 covering the wavelength range from the X-ray to the optical. ...The facilities included the telescopes of the CMO SAI MSU, the 2.3-m WIRO telescope, and the XRT and UVOT of Swift. We found that NGC 3516 brightened to a high state and could be classified as Sy1.5 during the late spring of 2020. We have measured time delays in the responses of the Balmer and He II 4686 lines to continuum variations. In the case of the best-characterized broad H-beta line, the delay to continuum variability is about 17 days in the blue wing and is clearly shorter, 9 days, in the red, which is suggestive of inflow. As the broad lines strengthened, the blue side came to dominate the Balmer lines, resulting in very asymmetric profiles with blueshifted peaks during this high state. During the outburst the X-ray flux reached its maximum on 1 April 2020 and it was the highest value ever observed for NGC 3516 by the Swift observatory. The X-ray hard photon index became softer, about 1.8 in the maximum on 21 Apr 2020 compared to the mean about 0.7 during earlier epochs before 2020. We have found that the UV and optical variations correlated well (with a small time delay of 1-2 days) with the X-ray until the beginning of April 2020, but later, until the end of Jun. 2020, these variations were not correlated. We suggest that this fact may be a consequence of partial obscuration by Compton-thick clouds crossing the line of sight.
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