A Model of the Dust Envelope of the Carbon Mira Star V CrB from Photometry,Infrared Spectroscopy,and Speckle Polarimetry

$$UBVJHKLM$$ photometry for the carbon Mira star V CrB are presented. The infrared observations were carried out in the time interval 1989–2018, while the $$U$$, $$B$$, and $$V$$ data were obtained in 2001–2014. The light and color curves are analyzed. The pulsation period of V CrB has been found to be $$355\overset{\textrm{d}}{.}2$$ in the infrared $$JHKLM$$ bands and $$352^{\textrm{d}}$$ for the optical $$BV$$ band. In the $$JHK$$ bands, apart from periodic pulsations, there are distinct sinusoidal variations in the average brightness level with a characteristic period of $${\sim}8300$$ 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 $$\tau_{K}=0.33$$, the inner and outer radii of the envelope are 8 and 40 000 AU, respectively. The envelope contains spherical carbon dust grains ($$3/4$$ by mass) and silicon carbide dust grains. Dust grains with a radius of 0.5 $$\mu$$m account for $$90\%$$ of the envelope mass. The remaining $$10\%$$ of the mass is accounted for by finer dust with a grain radius of 0.1 $$\mu$$m. Based on the observational data, we have estimated the bolometric flux from V CrB: $$2.6\times 10^{-7}$$ and $$5.1\times 10^{-7}$$ erg cm$${}^{-2}$$ s$${}^{-1}$$ at minimum and maximum light, respectively. The effective temperature of the star is $$T_{\textrm{max}}=3000$$ K at maximum light and $$T_{\textrm{min}}=2400$$ K at minimum light.     

Temporal variability in SO<Subscript>2</Subscript> exposures at Hawai’i Volcanoes National Park,USA

Sulfur dioxide measured at the Visitor’s Center of Hawai’i Volcanoes National Park, USA exhibits seasonal and diurnal patterns and is sensitive to rainfall, but the relationship between wind direction and SO₂ is too inconsistent to support deterministic predictions of hourly SO₂ based on hourly wind direction. Although SO₂ at the Visitor Center has usually been below regulatory levels, high SO₂ levels and adverse health effects remain a concern. This investigation identified patterns in hourly SO₂ based on wind direction, time of day, month, and rainfall occurrence using 4 years of hourly data. Empirical probabilities were investigated using a Bayesian approach. Winds from the volcanic vents were rare, but when they did occur SO₂ was elevated about half of the time. Conversely, half of the hours with elevated SO₂ occurred when volcanic vents were not directly upwind. Episodes of elevated SO₂ tended to occur during the months of November–March and between 8:00 a.m. and 5:00 p.m. Rainfall was associated with a marked reduction in SO₂ (29–81% depending on wind direction). Individuals that wish to avoid exposure to volcanic fumes can take these patterns into account.     

IR photometry of the symbiotic star BF Cyg: Detection of the red giant’s ellipsoidal brightness variability

We present the results of our IR photometric observations of the classical symbiotic star BF Cyg acquired in 1978–2003. The variability range in the J and K bands was ～0.2^m. A periodic component in the cool star’s brightness variations is clearly visible, its period being half the orbital one and its J amplitude being ～0.15^m. This component is associated with the ellipsoidal shape of the red giant, which model calculations show fills its Roche lobe. This is required in order to reproduce ellipsoidal brightness variability with such a large amplitude: the calculated amplitude for a red giant filling 90% of its Roche lobe is half the observed value. At the same time, it was not possible to confidently chose the optimum component-mass ratio, q = M _giant /M_hot, and orbital inclination, i, from possible values in the ranges q = 2–4, i = 70°–90°. Including the contribution from the hot radiation sources (the hot component and ionized envelope), which vary with a period equal to the orbital period, has a considerable influence on the estimated parameters associated with the red giant’s ellipsoidal brightness variations, and this contribution cannot be neglected. The deviations of the observed from the calculated light curve are irregular, with the rms deviation being σ(O-C) ≈ 0.04^m.     

North Atlantic sea surface temperatures and their relation to the North Atlantic Oscillation during the last 230?years

August Sea Surface Temperatures (aSSTs) based on fossil diatom assemblages are generated with 2?year average resolution from a 230-year-long sediment core (Rapid 21-12B), from the Reykjanes Ridge in the subpolar North Atlantic. The results indicate a warming trend of ~0.5°C of the surface waters at the Reykjanes Ridge for the last 230?years. Superimposed on this warming trend there is a multidecadal to decadal aSST variability of up to 1°C. The interval from the 1770s to the 1830s represents the coldest period, whereas ~1860?C1880 represents the warmest period during the last 230?years. The last 25?years is characterized by a warming trend showing strong decadal aSST variability with several warm years, but also the coldest years since the 1820s. The time of these cold years in the mid-1970s, -1980s and -1990s correspond with the documented great salinity anomalies (GSA) in the North Atlantic suggesting increased fluxes of cold, low-salinity waters from the Arctic during the last decades. The aSST record and the August North Atlantic Oscillation (aNAO) index show similar multidecadal-scale variability indicating a close coupling between the oceanic and atmospheric patterns. The aSST record shows a negative correlation with the aNAO indicating cold aSST during the positive aNAO trend and vice versa. Results suggest that the wind driven variation in volume fluxes of the North Atlantic surface waters could be the major mechanism behind the observed relationship.     

Spectroscopy and photometry of the symbiotic nova PU Vul during its nebular phase and minimum of 2007

We present the results of our analysis of the spectrophotometric and photometric data for the symbiotic nova PU Vul acquired in 2001–2008. The continuum in the optical observed in 2006–2008 cannot be reconciled with a standard model including light from the cool component, hot component, and nebula. The hot component’s temperature increased to 194 000 K by 2008, while its luminosity decreased by a factor of ten compared to the plateau of 1979–1991. The evolution of the hot component as reflected by the Hertzsprung-Russell diagram does not agree with a theoretical model describing the evolution of a thermonuclear outburst in a white-dwarf envelope. We estimate the mass of the hot component to be 0.5M _⊙ based on the luminosity of the hot component during the plateau stage. Our spectroscopy reveals periodic continuum-flux variations due to brightness variability of the cool component, with an amplitude of at least 2 ^m at 7000 ?. The spectral type of the cool component in 2008 was M6.3.     

Spectroscopic and photometric characteristics of stars in the field of the cluster vdB 130

The observational data for 24 stars toward the young cluster vdB 130 are analyzed. The spectroscopic and photometric BV RIJHK observations have been carried out with the following telescopes: 6-m at the Special Astrophysical Observatory of the Russian Academy of Sciences, 60-cm at the Southern Station of the Moscow State University, and 2.5-m at the Caucasus Observatory of the Sternberg Astronomical Institute of theMoscow State University. Nine stars previously selected as cluster members have been found to belong to different subtypes of type B. A minimum color excess toward the cluster, E(B ? V) = 0.9 mag, has been revealed for the vdB 130 stars lying outside the molecular cloud. Maximum color excesses, E(B ? V) = 1.3?1.4 mag, have been found in the spectra of cluster stars 1r and 5r observed in dust blobs. Inside the cluster R _v is shown to differ from the standard one. The overwhelming majority of the remaining investigated stars belong to late types and have minor color excesses (≤0.3) typical of close distances.