共查询到20条相似文献，搜索用时 31 毫秒
1.
I. S. Savanov 《Astronomy Reports》2009,53(11):1032-1038
We present our analysis of photometry for the FK Com star HD 199178 (V1794 Cyg). The V-band light curves are used to restore the distribution of temperature inhomogeneities on the stellar surface. The spots on
the surface of HD 199178 are concentrated at two preferred longitudes separated by 0.5 in phase (180° in longitude). In addition
to the quasi-periodic switching of the most active area between these two longitudes, which occurs in cycles of 2.1–2.4 or
4.1 years, we suspect that the two active areas moved toward each other across the stellar surface, possibly merging into
a single formation. The detected cycle in the star’s brightness variations of about 8.0 years is also clearly visible in variations
of the star’s spottedness. Themagnetic activity of the FK Com star HD199178 is in many ways similar to that observed for the
prototype of this group. 相似文献
2.
I. S. Savanov 《Astronomy Reports》2011,55(4):341-346
Unique high-accuracy 33.5-day continuous photometric observations of the KOI 877 and KOI 896 systems are used to study their
surface inhomogeneities and trace the evolution of spots over two to three rotational periods. These systems are two of five
candidate multi-planet objects. We found evidence for the existence of two active longitudes on the surfaces of KOI 877 and
KOI 896, separated by 165° and 135°, respectively. The fraction of the surface area covered by the spots is similar to the
solar one, and comprises about 0.6–1.1% of the total visible surfaces of the stars. A switch of the active longitudes likely
occurred in KOI 877 during the observation period. Calculated maps of surface temperature inhomogeneities may be helpful for
more accurate derivations of the parameters of planetary systems. 相似文献
3.
I. S. Savanov 《Astronomy Reports》2011,55(9):801-809
The activity of the K dwarf KIC 8429280 (TYC 3146-35-1) has been studied. Unique high-precision photometric observations of
this object obtained with the KEPLER space telescope suggest a pronounced amplitude modulation of the brightness of the star,
and have made possible the analysis of surface-temperature inhomogeneities. The evolution of active regions on the surface
of KIC 8429280 has been traced during 105 rotation periods. Evidence has been found for the existence of two active longitudes
on the surface of KIC 8429280, separated by approximately 180°. The motion of the active longitudes on the surface of KIC
8429280 is complex and unstable. At some times, the active regions moved together in longitude with the rotation of the star,
while they moved in opposite directions at other time. The less active region sometimes disappeared completely, and only one
active region was observed on the stellar surface. The area of the spotted surface S is 4% of the visible stellar surface for the adopted inclination of the rotation axis of the star to the line of sight, i = 60°. The periodicity for variations in S is no less than 90 d. The timescale for the change in the amplitude of the brightness variations is 30 d. Three epochs of
alternation of the active longitudes are close in time to three of four firmly established minima in the amplitudes of the
brightness variations. The results of the light-curve analysis for KIC 8429280 are compared to results obtained for the young
active solar-type star Corot-Exo-2, which has a similar light curve with a pronounced modulation. 相似文献
4.
A. V. Kozhevnikova V. P. Kozhevnikov I. Yu. Alekseev I. A. Yushkov A. A. Dorogov 《Astronomy Reports》2012,56(4):281-289
We present the results of new multicolor photometry of the chromospherically active binary CG Cyg acquired in 2005–2009 (136
hours of observations). The light curves for each season reveal rotational brightness modulation due to spots that varies
in amplitude and phase from season to season. We have determined the longitudes of spotted areas: for each season, they were
located on the primary, close to the line joining the centers of the components. The longitude distribution of spots was analyzed
for 44 years of observations of CG Cyg using all data available in the literature. The active longitudes of CG Cyg are not
fixed at the quadratures, as was believed earlier: most of the time (1965–2003), the spots were concentrated at two active
longitudes at the quadratures, at orbital phases 0.28±0.06 and 0.70±0.08, but, during a shorter time after 2004, they were
located along the line joining the component centers, at orbital phases 0.50 ± 0.04 and 0.93 ± 0.03. We detected a switch
of the active longitude by 180° during 1.5 months in 2008, accompanied by an increase in the amplitude of the rotational brightness
modulation and only a slight increase in the star’s spotted area (by 5%). Our analysis of archive data reveals that switches
of the active longitude during time intervals of 1–1.5 months were observed three times during the entire observational history
of CG Cyg (in 1991, as well as in our observations of 2003 and 2008). All these switches were accompanied by similar phenomena:
an increase in the amplitude of the rotational brightness modulation (by 0.06
m
, 0.02
m
, and 0.04
m
) and an increase in the spotted area (by 79%, 11%, and 5%). We used a zonal spot model to reconstruct the parameters of the
spotted regions on CG Cyg. At all our observing epochs, the spots were located at low latitudes, in a region that was symmetric
about the equator, 10° to 14° wide on either side. The spots are cooler than the surrounding photosphere by 2000 K. The spotted
area varied only slightly from season to season, comprising 13%–15% of the surface area of the star, close to the historic
spottedness maximum for the CG Cyg system. 相似文献
5.
Active regions on the surfaces of the chromospherically active stars GSC 08923-01147 and GSC 08933-01802 are found by reconstructing
the surface-temperature inhomogeneities using the V light curves, obtained from observations performed during the ASAS-3 project. Up to one-third of the total observed area
of the stellar surfaces was covered by spots. In GSC 08923-01147, the spotted fraction decreased from 0.31 to 0.05 during
the observation period, while it varied within 0.2–0.3 during four years in GSC 08933-01802. The detected phases of active
longitudes tend to concentrate near two positions separated by about half a period. The active regions in GSC 08933-01147
became closer or further apart on a time scale of 4.8 years. The maximum separations of the longitudes Δφ
long were maximum when the amplitude of the brightness variability reached a minimum. During the transition of the star from a
minimum-brightness to an enhanced-brightness state, the longitude of the more active region switched. The brightness variability
of GSC 08933-01802 was more substantial (ΔV }~ 0.55
m
−0.06
m
). For some time, only one extended active region was present on the stellar surface, while two regions were usually present.
No switch of the active longitudes was detected. The more active region monotonically moved over the surface of the star,
causing the longitudes of the active regions to drift together. This monotonic change in the position of the more active longitude
ceased at the minimum of the brightness-variation amplitude. 相似文献
6.
I. S. Savanov 《Astronomy Reports》2009,53(10):941-949
We have analyzed light curves from the MOST satellite for the two active dwarfs ɛ Eri and κ Cet. Our maps of the stellar surface-temperature inhomogeneities were obtained with no a priori assumptions about the shape,
configuration, and number of spots. We find variations of the surface-temperature inhomogeneities with time, also on time
scales about equal to their rotation periods. We consider a model of a spotted star with two types of surface inhomogeneities—spots
and related plage fields—and demonstrate that the best agreement between the theoretical and observed light curves is achieved
for small ratios of the plage-field area to the area of cool spots. This conclusion indicates that long-term brightness variations
of stars younger than the Sun are mainly due to variable spots on their surfaces, while the contribution from plage fields
becomes more significant for older stars. 相似文献
7.
I. S. Savanov 《Astronomy Reports》2010,54(5):437-445
Continuous photometric observations of the young active solar-type star Corot-Exo-2a using the “Corot” space telescope obtained over 142 days were used to analyze the star’s surface temperature inhomogeneities and to monitor their continuous evolution. This analysis was based on the iPH code, which reconstructs the distribution of temperature inhomogeneities on the surface of a star based on its light curve in a two-temperature approximation. We identified five time intervals in the positions of active areas, with corresponding flip-flop events, interpreted as activity periods. Their durations were between 55 and 15 days. The time scale for the active-longitude flip-flops of Corot-Exo-2a is a few tens of days, rather than years, as for other stars studied earlier. We detected motions of the active longitudes, possibly indicating differential rotation of the star. The phenomenon of flip-flops in the positions of active longitudes has a complex character. This is the first case apart fromthe Sun where we are able to follow the appearance and development of temperature inhomogeneities on a stellar surface in such detail. We determined typical timescales for variations of the activity parameter of the star in the ranges 17–20, 28–32, 33–38, and 51–55 days, which characterize changes of the brightness variation amplitude, the spotted surface area, positions of active areas, and brightness variations. 相似文献
8.
High-accuracy photometric observations obtained with the Kepler Space Telescope are used to identify candidate FK Com stars-a very rare group of single, rapidly rotating, chromospherically active G-K stars. Published data for more than 40 000 stars are used with available Kepler observations from the Q3 time interval to select four stars with temperature ranges, surface gravities, and rotation periods consistent with those of FK Com stars. These stars also display brightness variations with considerable amplitudes, possibly testifying to the presence of appreciably spotting on their surfaces. The rotation periods of these stars are determined, and the parameters of their differential rotation estimated. The locations (longitudes) of the dominant active regions on the stellar surfaces are identified. In all cases, the active longitude does not remain constant, andmoves across the stellar surface with time. In general, the character of this activeregion movement is the same as that found earlier for FK Com and HD 199178. These displacements are characterized by monotonic motions over hundreds of days, as well as changes in the positions by about 180° (“flip-flops”) or phase shifts not exceeding 0.4 in phase. The number of active-longitude position changes during the studied time interval ranges from one for KIC 11862915 to seven for KIC 5785906 (five phase shifts are also detected for the latter star). The time scale for the position changes of the active longitudes is from 1500 days (about 4 years) to 200 days (0.54 years), comparable to the reported time intervals between flip-flops for FK Com (from 0.8 to 4.4 years). The duration of the stellar activity cycles are estimated by analyzing the amplitude spectrum for changes in the brightness-variation amplitudes for datasets covering a single rotation period. The photometric variations of the stars on various time scales (from the rotation period, which reveals the presence of surface temperature inhomogeneities, to activity cycles lasting for several years) are similar to those derived for FK Com and other stars of this type. The need for spectroscopic observations of the selected candidates to establish whether they are single (do not show signs of binarity), look for emission lines of chromospheric origin, estimate the lithium abundances, and determine the stellar rotation velocities from spectral-line profiles is noted. 相似文献
9.
I. S. Savanov 《Astronomy Reports》2012,56(9):722-729
The activity of V410 Tau, a T Tauri star with periodic brightness variations, is studied. The evolution of spots on the star??s surface over 46 years is investigated by reconstructing inhomogeneities in the stellar surface temperature based on photometric measurements. Analysis of the distribution of filling factors f as functions of time and longitude on the star??s surface can be used to trace changes in the location of the dominant active area. In some cases, a second active area (longitude) separated by about 180° is detected. No reliable manifestations of switching of the positions of the active areas were detected. The position of the active area was stationary and the position of minimum brightness remained unchanged during a time interval of 4800 days (about 13 years), which ended by the end of 2002. Though the position of the brightness minimum remained virtually constant, the light-curve shape (asymmetry) and the spot ??outline?? in the reconstructed temperature maps exhibited variations. The star possesses considerable cool spots on its surface, whose fractional area is typically 32% and varies between 27% and 40%. Variations of the star??s brightness and spottedness on time scales of 4.8?C5.5 years are most prominent. 相似文献
10.
Continuous 123.87-day observations with the “Kepler” space telescope are used to study the activity of the fully convective,
low-mass M dwarf LHS 6351. The axial-rotation period of the star is 3.36 day. High-precision photometric observations of LHS
6351 enabled studies of its surfacetemperature inhomogeneities and their evolution. The difference in the longitudes of active
regions increased from 120° at the beginning to 207° at the end of the observations, for i = 60° (and from 156° to 198° for i = 30°). This variation of the locations of the spots on the stellar surface provides evidence for differential rotation of
the star. According to our estimates, the rate of displacement of the active regions is (0.006–0.014) ± 0.002 rad/day. Assuming
i = 60°, the total area of spots S decreased, on average, from 1.2% to 0.92% of the total visible surface of the star; if i = 30°, this area decreased from 1.8% to 1.0%. We compared manifestations of the magnetic activity of LHS 6351 with the properties
of the fully convective M dwarfs V374 Peg and GJ 1243, studied earlier. We derived the dependence of ΔΩ on the Rossby number
for these M dwarfs, and identified two groups of stars with differing mass and differential rotation. 相似文献
11.
The photometric variability of the uniqueMdwarf flare star GJ 1243 (KIC 9726699) is investigated using the most complete set of observationalmaterial obtained with the Kepler Space Telescope. The analysis is based on 49 487 individual brightness measurements obtained during an interval of 1460 days (nearly four years). The periodicity of the brightness variations with the period Pphot = 0.59261 ± 0.00060d is confirmed. The temperature inhomogeneities on the stellar surface reconstructed from the light curve are used to drive maps of these surface-temperature inhomogeneities (of the filling factor f). The resulting maps are used to determine the positions of active regions. Analysis of the surface-temperature maps for GJ 1243 led to the conclusion that the positions of spots on the stellar surface displayed appreciable evolution during the analyzed time interval. The maximum value for the lower limit on the differentialrotation parameter ΔΩ is 0.0022 rad/day. This more accurate estimate of ΔΩ is lower than the values presented earlier by Davenport et al. [1] (0.0058 and 0.0036 rad/day), due to the more accurate account of variations in the positions of the most active longitude in the current study. However, the differentialrotation estimate obtained in [1] using a method based on fitting the evolution of spots using twodimensional Gaussian functions essentially coincides with the new estimate presented here. The fractional area of the total spotted surface S of the star during the observing interval considered varied from 7 to 2%. The amplitude of the brightness variability of the star slowly decreased, varying in the range 1.6?0.5%. Overall, the position of GJ 1243 in spottedness–age, spottedness–rotation period, and spottedness–Rossby number diagrams agrees very well with the general character of the dependences displayed in earlier studies of M dwarfs. 相似文献
12.
I. S. Savanov 《Astronomy Reports》2009,53(10):950-956
We have analyzed light curves from the MOST satellite for the two active dwarfs ? Eri and κ Cet. Our maps of the stellar surface-temperature inhomogeneities were obtained with no a priori assumptions about the shape, configuration, and number of spots. We find variations of the surface-temperature inhomogeneities with time, also on time scales about equal to their rotation periods. We consider a model of a spotted star with two types of surface inhomogeneities—spots and related plage fields—and demonstrate that the best agreement between the theoretical and observed light curves is achieved for small ratios of the plage-field area to the area of cool spots. This conclusion indicates that long-term brightness variations of stars younger than the Sun are mainly due to variable spots on their surfaces, while the contribution from plage fields becomes more significant for older stars. 相似文献
13.
Hydrological impacts from climate change are of principal interest to water resource policy-makers and practicing engineers.
Predictive climatic models have been extensively investigated to quantify the impacts. Palaeoclmatic investigations, on the
other hand, show unequivocal and strong periodicity of climate variations in proxy evidence. Yet how to use the periodicity
in future hydroclimatic timing and forecasting has received less attention. This paper examines the periodicity in Pleistocene–Holocene
glacial–interglacial events and in modern precipitation records, and discusses a way in which the periodicity is used for
hydroclimatic predictions. The analysis, based on published CO2, ΔT (δ2H) and δ18O proxy data of polar ice cores and deep oceanic benthic fossils, shows a periodicity in a ~100, ~40 or 25 kyear duration
consistent with Milankovitch orbital regulations during the glacial–interglacial periods. On a fine time scale, millennium
and multi-decadal periodicity is observed in high-resolution proxy variations of Greenland ice cores and in instrumental precipitation
records of the contiguous USA. A basic periodicity of decadal and multi-decadal changes in ~20 and ~10–15 year duration is
apparent in wavelet frequency analysis of both ice core proxy and precipitation data. While the kyear-scale periodicity is
found of global prevalence, the millennium and decadal variations vary in space and are region-specific. Based on these findings,
a generalized time-downscaling hierarchy of periodicity is proposed as a potential approach for timing and forecasting future
hydroclimatic conditions at a resolution relevant to the water resources engineering and management. 相似文献
14.
A. V. Kozhevnikova I. Yu. Alekseev P. A. Heckert V. P. Kozhevnikov 《Astronomy Reports》2007,51(11):932-946
We present the results of multicolor photometry of the two spotted, short-period, late-type RS CVn stars BH Vir and WY Cnc. We have derived the parameters of the binaries’ components, and refined their masses, radii, and luminosities. A strong flare of WY Cnc was detected for the first time, and pre-flare variations of the star’s activity studied. Our observations and published data spanning 40 years are analyzed using a zone starspot model. We demonstrate that the spots are always concentrated near the equators and at intermediate latitudes, with maximum spotted areas as large as 29% for BH Vir and 21% for WY Cnc. The temperature differences between spotted regions and the quiet photosphere were 2300 K (BH Vir) and 1800 K (WY Cnc). The detected long-term brightness variations of BH Vir suggest the existence of an activity cycle with a probable period of 22 years. Both stars have starspots concentrated at two active longitudes separated by approximately half of the orbital period during all the studied seasons; these longitudes remained the same (0° and 184°) for BH Vir over 40 years, whereas they migrated in the direction of the stellar rotation at a rate of 3.8°/yr for WY Cnc, suggesting a cycle of 47 years for the migration of the active longitudes. 相似文献
15.
The activity of the central star of the Kepler-32 planetary system is studied using continuous 1141-day observations with the Kepler Space Telescope. The Kepler-32 system includes a slowly rotating Mdwarf (rotational period of 37.8 d) with a mass of 0.54M ⊙ and five planets. One of the unique properties of the system is its compactness: the orbits of all five planets are less than a third of the size of the orbit of Mercury; the planet closest to the star is separated from it by only 4.3 stellar radii. Surface-temperature inhomogeneities of the central star are studied using precise photometric observations of Kepler-32, and their evolution traced. In total, 42 624 individual brightness measurements in the 1141-day (3.1-year) observing interval were selected for the analysis. The calculated amplitude power spectra for the first and second halves of the interval of the Kepler-32 observations indicate appreciable variability of the photometric period, corresponding to the evolution of active regions at various latitudes on the stellar surface. Evidence for the existence of two active regions on the stellar surface separated in phase by 0.42 has been found. Time intervals in which the longitudes of the active regions changed (“flip-flops”) with durations of the order of 200–300 days have been established. The spotted area of the star was, on average, about 1% of the total visible surface, and varied from 0.3 to 1.7%. The results for the dwarf Kepler-32 are compared with those from a spectropolarimetric survey of 23 M dwarfs, including both fully convective stars and stars with weakly radiative cores. For a more detailed comparison, temperature inhomogeneities on the surface of one of the survey stars, DS Leo, was reconstructed using the ground-based observations (316 individual measurements of the V-band brightness of the star during seven observing seasons in an all-sky automated survey). The general properties and evolution of the active regions on DS Leo and Kepler-32 are considered. The positions of the active regions on the surface of Kepler-32 yields no evidence for differential rotation of this star. The possibility of detecting the magnetic field of Kepler-32 is proposed. The analysis of the photometric data for Kepler-32 are also compared to the previous results for the fully convective, low-mass M dwarfs GJ 1243 and LHS 6351. This demonstrates that the observed manifestations of activity on Kepler-32 correspond to those for active G-K stars and to M dwarfs with masses of the order of 0.5M ⊙, rather than Mdwarfs with masses from 0.2 to 0.5M ⊙. 相似文献
16.
The spatial and temporal brightness distributions of the Fe XIV 530.3 nm coronal green line (CGL) and cyclic variations of these distributions are analyzed for a long time interval covering more than five 11-year cycles (1943–2001). The database of line brightnesses is visually represented in the form of a movie. Substantial restructuring of the spatial distribution of the CGL brightness occur over fairly short time intervals near the so-called reference points of the solar cycle; such points can be identified based on various sets of solar-activity indices. Active longitudes are observed in the CGL brightness over 1.5–3 yr. Antipodal and “alternating” active longitudes are also detected. The movie can be used to compare the CGL brightness data with other indicators of solar activity, such as magnetic fields. The movie is available at http://helios.izmiran.rssi.ru/hellab/Badalyan/green/. 相似文献
17.
N. I. Bondar’ 《Astronomy Reports》2017,61(2):130-137
Photometric data covering 1994–2009, obtained at the Crimean Astrophysical Observatory or retrieved from the ASAS and SuperWASP catalogs, were used to analyze the brightness variations of the rapidly rotating star V833 Tau, whose activity level is close to saturation. Combined with previously published results, these data represent for the first time all stages in the development of the star’s 19- year activity cycle. The photometric period and rotational-modulation amplitude for different epochs are determined, and the qualitative pattern of the spots is considered. The photometric period is close to the orbital period, but always exceeds it, indicating that surface inhomogeneities are located far from the equatorial plane. With the high spottedness of the star, reaching 28% at the cycle maximum, the rotationalmodulation amplitude is 0.05?0.1 m , and increases during the growth and decline phases of the 19-year cycle. The rotational modulation is due to spots with higher latitudes than in the case of the Sun, and concentrating on active longitudes. 相似文献
18.
I. S. Savanov 《Astronomy Reports》2010,54(3):228-233
V-band light-curves are used to reconstruct the temperature inhomogeneities on the surface of the young T Tauri star Par 1724.
The spots on the surface of Par 1724 are concentrated close to two preferred longitudes separated by 180° (0.5 in phase).
These results provide evidence that Par 1724 may be the youngest star fow which a switch of the active longitudes is detected. 相似文献
19.
We apply Fourier and wavelet analyses to the precipitation and sunspot numbers in the time series (1901–2000) over Australia
(27°S, 133°E), Canada (60°N, 95°W), Ethiopia (8°N, 38°E), Greenland (72°N, 40°W), United Kingdom (54°N, 2°W), India (20°N,
77°E), Iceland (65°N, 18°W), Japan (36°N, 138°E), United States (38°N, 97°W), South Africa (29°S, 24°E) and Russia (60°N,
100°E). Correlation analyses were also performed to find any relation among precipitation, sunspot numbers, temperature, and
cloud-cover at the same spatial and temporal scale. Further correlations were also performed between precipitation with electron
and proton fluence at the time interval, 1987–2006. All these parameters were considered in annual and seasonal scales. Though
correlation study between precipitation and other parameters do not hint any linear relation, still the Fourier and wavelet
analyses give an idea of common periodicities. The 9–11 year periodicity of sunspot numbers calculated by Fourier transform
is also confirmed by wavelet transform in annual scale. Similarly, wavelet analysis for precipitation also supports the short
periods at 2–5 years which is verified by Fourier transform in discontinuous time over different geographic regions. 相似文献
20.
We used continuous observations with the KEPLER space telescope during 44.45 days to study the activity of the fully convective
low-mass M dwarf GJ 1243. The star’s rotational period is 0.593 days. Our precision photometry of GJ 1243 made it possible
to study its surface temperature inhomogeneities and follow their evolution. We find evidence for two active longitudes on
the surface of the star, separated by 203° in longitude or 0.56 in phase. The position of spots on the surface was found to
be very stable during the analyzed 74 rotation periods. Assuming that the rotational axis is inclined to the line of sight
by i = 60°, the total spotted area S is, on average, 3.2% of the total visible stellar surface, and increased by 0.7% in 100 days; if i = 30°, the area is S = 5.6%. The change in S is due to an increase in the area of the smaller active region. We compare the magnetic-activity features of GJ 1243 and
another fully convective star, V374 Peg. 相似文献