ABSTRACT
We investigate the spatial regularity in the distribution of the young stellar population along spiral arms of three late-type spiral galaxies: NGC 895, NGC 5474, and NGC 6946. This study is ...based on an analysis of photometric properties of spiral arms using Galaxy Evolution Explorer ultraviolet, optical UBVRI, H α, and 8 μm IRAC infrared surface photometry data. Using the Fourier analysis approach, we found features of spatial regularity or quasi-regularity in the distribution of the young stellar population or (and) regular chains of star formation regions in all arms of NGC 895, NGC 5474, and NGC 6946 with characteristic scales of spacing from 350 to 500 pc in different arms, and (or) scales that are multiples of them. These characteristic scales are close to those found earlier in NGC 628, NGC 6217, and M100.
ABSTRACT
We present the results of a study of young unresolved stellar groupings (clusters, OB associations, and their complexes) associated with H ii regions, based on the coupling of spectroscopic, ...photometric and H α spectrophotometric observations of star formation regions. Along with our own observations, we use a part of the spectroscopic and H α data from the literature and open data bases. The study is based on the catalogue of 1510 star formation regions with ages ∼10–20 Myr in 19 spiral galaxies, compiled by us earlier. We study the morphology of stellar groupings and their relation with the associated H α emission region. Extinctions, gas chemical abundances, and sizes of star formation regions are measured. Using numerical simple stellar population models computed for metallicities fixed from observations to intrinsic colours of the studied star formation regions, we estimated ages and masses of stellar population of 400 young stellar groupings. Different relations between observational and physical parameters of the young stellar population in star formation regions are discussed.
ABSTRACT
We study the propagation of star formation based on the investigation of the separation of young star clusters from H ii regions nearest to them. The relation between the separation and U − ...B colour index (or age) of a star cluster was found. The average age of star clusters increases with the separation as the 1.0–1.2 power in the separation range from 40 to 200 pc and as the 0.4–0.9 power in the range of 100–500 pc in the galaxies with symmetric morphology. The galaxies with distorted asymmetric disc structure show more complex and steeper (power >1.2 at separations from 40 to 500 pc) dependence between the age and the separation. Our results confirm the findings of previous studies on the dominant role of turbulence in propagation of the star formation process on spatial scales up to 500 pc and on time-scales up to 300 Myr. On a smaller scale (≤100 pc), other physical processes, such as stellar winds and supernova explosions, play an important role along with turbulence. On the scale of stellar associations (100–200 pc and smaller), the velocity of star formation propagation is almost constant and it has a typical value of a few km s−1.
In 2015–2021 we carried out observations of the Seyfert 1 galaxy (SyG 1) NGC 7469 in Bessell
filters with the 1.5-m telescope of the Maidanak Observatory, which have continued the monitoring of NGC ...7469 since 1990. We took
CCD frames and performed standard frame processing, including bias correction, sky background subtraction, flat fielding, cosmic-ray particle removal, etc. All our data were obtained on CCD cameras with deep cooling and subarcsecond seeing. We carried out the calibrations using several standard stars in the same frame as the galaxy. The results of our photometry in a 13.5 arcsec aperture are presented graphically in the visibility windows of the observed period. A slow (S) flare was detected on the constructed variability curves in the
filters; a slow increase in brightness is observed since 2015, reaching a maximum in 2019. The amplitude of the S flare is 0.5 mag in the
filter and decreases to zero in the
filter. On the color–color
diagrams the colors in a 5 arcsec aperture are bluer than those in a 30 arcsec aperture.
Quasar microlensing offers a unique opportunity to resolve tiny sources in distant active galactic nuclei and study compact object populations in lensing galaxies. We therefore searched for ...microlensing-induced variability of the gravitationally lensed quasar QSO 2237+0305 (Einstein Cross) using 4374 optical frames taken with the 2.0 m Liverpool Telescope and the 1.5 m Maidanak Telescope. These gVrRI frames over the 2006–2019 period were homogeneously processed to generate accurate long-term multi-band light curves of the four quasar images A–D. Through difference light curves, we found strong microlensing signatures. We then focused on the analytical modelling of two putative caustic-crossing events in image C, finding compelling evidence that this image experienced a double caustic crossing. Additionally, our overall results indicate that a standard accretion disc accounts reasonably well for the brightness profile of UV continuum emission sources and for the growth in source radius when the emission wavelength increases: Rλ ∝ λα, α = 1.33 ± 0.09. However, we caution that numerical microlensing simulations are required before firm conclusions can be reached on the UV emission scenario because the VRI-band monitoring during the first caustic crossing and one of our two α indicators lead to a few good solutions with α ≈ 1.
We present a study of complexes of young massive star clusters (YMCs), embedded in extragalactic giant H ii regions, based on the coupling of spectroscopic with photometric and spectrophotometric ...observations of about 100 star-forming regions in seven spiral galaxies (NGC 628, NGC 783, NGC 2336, NGC 6217, NGC 6946, NGC 7331, and NGC 7678). The complete observational data base has been observed and accumulated within the framework of our comprehensive study of extragalactic star-forming regions. This paper presents the last part of either unpublished or refreshed photometric and spectrophotometric observations of the galaxies NGC 6217, NGC 6946, NGC 7331, and NGC 7678. We derive extinctions, chemical abundances, continuum, and line emissions of ionized gas, ages, and masses for cluster complexes. We find the YMC complexes to have ages no greater than 10 Myr and masses between 104 M⊙ and 107 M⊙, and the extinctions A
V
vary between ∼0 and 3 mag, while the impact of the nebular emission on integrated broad-band photometry mainly is not greater than 40 per cent of the total flux and is comparable with accuracies of dereddened photometric quantities. We also find evidence of differential extinction of stellar and gas emissions in some clusters, which hinders the photometric determination of ages and masses in these cases. Finally, we show that young massive cluster complexes in the studied galaxies and open clusters in the Milky Way form a continuous sequence of luminosities/masses and colour/ages.
The source BL Lac exhibited an enhanced activity from August 2020 to July 2022. This activity peaked in July–August 2021. In this period the source reached historic brightness maxima in various ...energy ranges. Observations of this nonstandard maximum were carried out by the SAI staff of the Crimean Station of SAI and with the telescopes of the Caucasus Mountain Observatory (CMO SAI MSU). Optical and near-infrared photometric data as well as optical polarimetric data were obtained. When investigating the correlation between the optical and gamma-ray fluxes and between the optical and infrared fluxes, its high degree with an almost zero lag was confirmed—this means that the emission regions spatially coincide or are very close together. The degree of linear polarization in the investigated period changed in a wide range, reaching 20
, with an anticorrelation between the degree of linear polarization and the brightness of the object having been observed. A similar pattern of variation was also observed in the preceding flares of this object. The changes in the electric vector position angle (EVPA) show a dependence on the rate of change of the object’s brightness. The EVPA changed greatly during flares and slowly at the times of a slow change in the intensity.
The atmospheric activity of the sun and of stars of the solar-type is analyzed using observations from the HK-project at the Mount Wilson Observatory, California, and the Carnegie Planet Search ...Program at the Keck and Lick Observatories, as well as from the Magellan Planet Search Program at the Las Campanas Observatory. It is shown that a cyclical activity of the stars that is analogous to the 11-year solar activity cycle occurs in stars of spectral classes F, G, and K and is more pronounced in stars of class K. A comparative analysis of the solar-type stars with different levels of chromospheric and coronal activity confirms that the sun is one of the stars with a comparatively low level of atmospheric activity and that these stars have a minimal level of coronal emission and minimal variations in the fluxes of photospheric radiation.
We present the results of our multicolor
UBV RI
observations of NGC 7469, a type 1 Seyfert galaxy (SyG 1), in 2008–2014 at the Maidanak Observatory. Analysis of the long-term variability of NGC 7469 ...for two observing periods, 1990–2007 and 2008–2014, has shown the existence of yet another activity cycle of the slow component in 2009–2014 with an activity maximum in 2011–2012. We have studied the slow variability component in 2009–2014 and constructed the color–color (
U
−
B
), (
B
−
V
) diagrams for the variability maxima and minima of NGC 7469 in various apertures and for the blackbody gas radiation modeling the accretion disk radiation. It can be seen from the color–color diagram that the color of the nuclear part of NGC 7469 becomes bluer at maximum brightness, suggesting a higher temperature of the accretion disk. We have analyzed the X-ray variability of NGC 7469 in 2008 and 2009 in comparison with the activity minimum in 2003. The optical–X ray correlation coefficient in 2008 is close to 0.5. The weak correlation is explained by the influence of an SN 1a explosion in the circumnuclear part of NGC 7469, which manifests itself in the optical band but does not change the pattern of X-ray variability. Comparison of the variability data for 2009 shows an optical–X ray (
U
band–7–10 keV) correlation with a correlation coefficient of about 0.93. The correlation coefficient and the lag depend on the wavelength in the optical and X-ray bands. The lag between the X-ray and optical fluxes in 2009 is observed to a lesser extent in 2003.
A statistical analysis of published long-term photometric monitoring observations of the gravitationally lensed quasar PG 1115+080 in the optical is presented. This goal of this study is determining ...the time delay between variability of the quasar manifest in its various images. Light curves of the components of PG 1115+080 obtained in 2001–2006 at the Maidanak Observatory (Uzbekistan) are considered. A linear trend is observed in the light curves of all four components during 2006, with rapid brightness variations observed only in components A1 and C. This could be a consequence of microlensing or observational errors. Application of a modified cross-correlation method to the photometric data obtained in 2004–2005 yields the time delays
τ
BC
= 22
−3
+2
days,
τ
AC
= 12
−1
+2
days, and
τ
BA
= 10
−3
+2
days, in agreement with results obtained earlier by Schechter et al. and Barkana for 1995–1996 light curves using two different statistical-analysis methods. However, the new values of
τ
BA
and
τ
BC
differ from those obtained by Vakulik et al. using the same Maidanak Observatory data. The ratio
τ
AC
/
τ
BA
∼1.2, which is close to the values obtained by Barkana (∼1.13) and predicted by lens models (∼1.4); these differ from the values obtained by Schechter et al. (∼0.7) and Vakulik et al. (∼2.7).
PDF
