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Register a new userA deep decrease event in the brightness of the PMS star V350 Cep
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New photometric data from CCD UBVRI observations of the PMS star V350 Cep during the period from March 2014 to May 2017 are presented. In the period April-May 2016 we registered a deep fades event in the brightness of the star with amplitudes $Delta I$ = 1.75 mag, $Delta R$ = 1.69 mag, $Delta V$ = 1.77 mag and $Delta B$ = 2.16 mag. Simultaneously with the fades in the brightness, the change in the stars color indices has been observed. V350 Cep indicates the typical for stars of UXor type blueing effect during the deep minimum of brightness. During the second half of 2016 V350 Cep restores its brightness to a level close to the maximum. Since the star has been studied as a possible FUor object in previous studies, the possible cause of the deep decline is a decrease in the accretion rate. Another possible cause is obscuration from clumps of dust orbiting at the vicinity of the star.
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Results from UBVRI photometric observations of the pre-main sequence star GM Cep obtained in the period April 2011 - August 2014 are reported in the paper. Presented data are a continuation of our photometric monitoring of the star started in 2008. GM Cep is located in the field of the young open cluster Trumpler 37 and over the past years it has been an object of intense photometric and spectral studies. The star shows a strong photometric variability interpreted as a possible outburst from EXor type in previous studies. Our photometric data for a period of over six years show a large amplitude variability (Delta V ~ 2.3 mag.) and several deep minimums in brightness are observed. The analysis of the collected multicolor photometric data shows the typical of UX Ori variables a color reversal during the minimums in brightness. The observed decreases in brightness have a different shape, and evidences of periodicity are not detected. At the same time, high amplitude rapid variations in brightness typical for the classical T Tauri stars also present on the light curve of GM Cep. The spectrum of GM Cep shows the typical of classical T Tauri stars wide H/alpha emission line and absorption lines of some metals. We calculate the outer radius of the H/alpha emitting region as 10.4 +/-0.5 Rsun and the accretion rate as 1.8 x 10 E-7 Msun/yr.
Results from the BV(RI)c photometric observations of the young stellar object V2492 Cyg collected in the period from April 2018 to September 2020 are presented. These observations are a part of our monitoring of the star that began in 2010 and continuing to date. V2492 Cyg is located in the Pelican Nebula, and its variability was explained by both accretion and extinction events. The new photometric data show that the star continues to exhibit rapid irregular variability in all bands. In the period from March 2019 to May 2020, we registered a prolonged decrease event in the light curve of V2492 Cyg.
Based on new observations during 2015-2020 and published data, the unusual eruptive variables PV Cep and V350 Cep are examined. It is shown that PV Cep underwent a regular outburst followed by a drop in brightness that lasted overall from 2011 to 2019 and is still in a deep minimum. The outburst was accompanied by substantial changes in the intensity and profiles of a number of lines, including Ha, [SII], and [OI]. The forbidden lines generally have negative radial velocities and can be divided into four components, with variable velocities and relative intensities. V350 Cep essentially is at a maximum brightness level over the entire time and its spectrum is practically unaltered. The available data suggest that the pronounced P Cyg profile of the Ha line in the spectrum of V350 Cep appeared several years after the luminosity rise, in 1986. The luminosities of the stars in the current state are estimated to be 20 L(sun) and 3.3 L(sun), respectively. It is concluded that both stars may represent a so-called intermediate objects between the FUor and EXor classes.
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We analyze resolved stellar near-infrared photometry of 21 HST fields in M31 to constrain the impact of metallicity on the formation of carbon stars. Observations of nearby galaxies show that the carbon stars are increasingly rare at higher metallicity. Models indicate that carbon star formation efficiency drops due to the decrease in dredge-up efficiency in metal-rich thermally-pulsing Asymptotic Giant Branch (TP-AGB) stars, coupled to a higher initial abundance of oxygen. However, while models predict a metallicity ceiling above which carbon stars cannot form, previous observations have not yet pinpointed this limit. Our new observations reliably separate carbon stars from M-type TP-AGB stars across 2.6-13.7 kpc of M31s metal-rich disk using HST WFC3/IR medium-band filters. We find that the ratio of C to M stars (C/M) decreases more rapidly than extrapolations of observations in more metal-poor galaxies, resulting in a C/M that is too low by more than a factor of 10 in the innermost fields and indicating a dramatic decline in C star formation efficiency at metallicities higher than [M/H] $approx$ -0.1 dex. The metallicity ceiling remains undetected, but must occur at metallicities higher than what is measured in M31s inner disk ([M/H] $gtrsim$ +0.06 dex).
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