اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNew spectroscopic and polarimetric observations of the A0 supergiant HD92207
318
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Our recent search for the presence of a magnetic field in the bright early A-type supergiant HD92207 using FORS2 in spectropolarimetric mode revealed the presence of a longitudinal magnetic field of the order of a few hundred Gauss. However, the definite confirmation of the magnetic nature of this object remained pending due to the detection of short-term spectral variability probably affecting the position of line profiles in left- and right-hand polarized spectra. We present new magnetic field measurements of HD92207 obtained on three different epochs in 2013 and 2014 using FORS2 in spectropolarimetric mode. A 3sigma detection of the mean longitudinal magnetic field using the entire spectrum, <B_z>_all=104+-34G, was achieved in observations obtained in 2014 January. At this epoch, the position of the spectral lines appeared stable. Our analysis of spectral line shapes recorded in opposite circularly polarized light, i.e. in light with opposite sense of rotation, reveals that line profiles in the light polarized in a certain direction appear slightly split. The mechanism causing such a behaviour in the circularly polarized light is currently unknown. Trying to settle the issue of short-term variability, we searched for changes in the spectral line profiles on a time scale of 8-10min using HARPS polarimetric spectra and on a time scale of 3-4min using time series obtained with the CORALIE spectrograph. No significant variability was detected on these time scales during the epochs studied.
قيم البحث
اقرأ أيضاً
We present phase-resolved spectroscopy, photometry and circular spectropolarimetry of the eclipsing polar UZ Fornacis. Doppler tomography of the strongest emission lines using the inside-out projection revealed the presence of three emission regions:
from the irradiated face of the secondary star, the ballistic stream and the threading region, and the magnetically confined accretion stream. The total intensity spectrum shows broad emission features and a continuum that rises in the blue. The circularly polarized spectrum shows the presence of three cyclotron emission harmonics at $sim$4500 AA{}, 6000 AA{} and 7700 AA{}, corresponding to harmonic numbers 4, 3, and 2, respectively. These features are dominant before the eclipse and disappear after the eclipse. The harmonics are consistent with a magnetic field strength of $sim$57 MG. We also present phase-resolved circular and linear photopolarimetry to complement the spectropolarimetry around the times of eclipse. MeerKAT radio observations show a faint source which has a peak flux density of 30.7 $pm$ 5.4 $mu$Jy/beam at 1.28 GHz at the position of UZ For.
We present a study of the mass transfer and wind outflows of SS433, focusing on the so-called stationary lines based on archival high and low resolution optical spectra, and new optical multifilter polarimetry and low resolution optical spectra spann
ing an interval of a decade and a broad range of precessional and orbital phases. We derive $text{E(B-V)}=0.86pm0.10$ and revised UV and U band polarizations and polarization angles that yield the same position angle as the optical. The polarization wavelength dependence is consistent with optical-dominating electron scattering with a Rayleigh component in U and the UV filters; no polarization changes were observed during a flare event. Using profile orbital and precessional modulation of multiple lines we derive properties for the accretion disk, present evidence for a strong disk wind, determine its velocity structure, and demonstrate its variability on timescales unrelated to the orbit. We derive a mass ratio $q=0.37pm0.04$, and masses $text{M}_X=4.2pm0.4 text{M}_odot$, $text{M}_A=11.3pm 0.6 text{M}_odot$, and show that the A star fills its Roche surface. The O I 7772 r{A} and 8446 r{A} lines show different but related orbital modulation and no evidence for a circumbinary disk component. Instead, the spectral line profile variability can be understood with an ionization stratified outflow predicted by thermal wind modeling, which also accounts for an extended equatorial structure detected at long wavelength.
We present the results of our $UBV$ and $JHKLM$-photometry for the semiregular pulsating variable V1027~Cyg, a supergiant with an infrared excess, over the period from 1991 to 2015. Our search for a periodicity in the $UBV$ brightness variations has
led to several periods from $P=212^{d}$ to $P=320^{d}$ in different time intervals. We have found the period $P=237^{d}$ based on our infrared photometry. The variability amplitude, the light-curve shape, and the magnitude of V1027~Cyg at maximum light change noticeably from cycle to cycle. An ambiguous correlation of the $B-V$ and $U-B$ colors with the brightness has been revealed. The spectral energy distribution for V1027~Cyg from our photometry in the range 0.36 ($U$)-5.0 ($M$) $mu$m corresponds to spectral types from G8I to K3I at different phases of the pulsation cycle. Low-resolution spectra of V1027 Cyg in the range $lambda$4400--9200 AA were taken during 16 nights over the period 1995--2015. At the 1995 and 2011 photometric minima the stars spectrum exhibited molecular TiO bands whose intensity corresponded to spectral types M0--M1, while the photometric data point to a considerably earlier spectral type. We hypothesize that the TiO bands are formed in the upper layers of the extended stellar atmosphere. We have measured the equivalent widths of the strongest absorption lines, in particular, the infrared Ca~II triplet in the spectrum of V1027~Cyg. The calcium triplet (Ca T) with $W_{lambda}(mathrm{Ca~T})=20.3pm1.8$ AA as a luminosity indicator for supergiants places V1027 Cyg in the region of the brightest G--K supergiants. V1027 Cyg has been identified with the infrared source IRAS~20004+2955 and is currently believed to be a candidate for post-AGB stars. The evolutionary status of the star and its difference from other post-AGB objects are discussed.
Massive stars play a significant role in the chemical and dynamical evolution of galaxies. However, much of their variability, particularly during their evolved supergiant stage, is poorly understood. To understand the variability of evolved massive
stars in more detail, we present a study of the O9.2Ib supergiant $zeta$ Ori Aa, the only currently confirmed supergiant to host a magnetic field. We have obtained two-color space-based BRIght Target Explorer photometry (BRITE) for $zeta$ Ori Aa during two observing campaigns, as well as simultaneous ground-based, high-resolution optical CHIRON spectroscopy. We perform a detailed frequency analysis to detect and characterize the stars periodic variability. We detect two significant, independent frequencies, their higher harmonics, and combination frequencies: the stellar rotation period $P_{mathrm{rot}} = 6.82pm0.18$ d, most likely related to the presence of the stable magnetic poles, and a variation with a period of $10.0pm0.3$ d attributed to circumstellar environment, also detected in the H$alpha$ and several He I lines, yet absent in the purely photospheric lines. We confirm the variability with $P_{mathrm{rot}}$/4, likely caused by surface inhomogeneities, being the possible photospheric drivers of the discrete absorption components. No stellar pulsations were detected in the data. The level of circumstellar activity clearly differs between the two BRITE observing campaigns. We demonstrate that $zeta$ Ori Aa is a highly variable star with both periodic and non-periodic variations, as well as episodic events. The rotation period we determined agrees well with the spectropolarimetric value from the literature. The changing activity level observed with BRITE could explain why the rotational modulation of the magnetic measurements was not clearly detected at all epochs.
We present a comprehensive study of a series of recurrent jets that occurred at the periphery of the NOAA active region 12114 on 2014 July 7. These jets were found to share the same source region and exhibited rotational motions as they propagated ou
tward. The multi-wavelength imaging observations made by the AIA and {it IRIS} telescopes reveal that some of the jets contain cool plasma only, while some others contain not only cool but also hot plasma. The Doppler velocities calculated from the {it IRIS} spectra show a continuous evolution from blue to red shifts as the jet motions change from upward to downward. Additionally, some jets exhibit opposite Doppler shifts on their both sides, indicative of rotating motions along their axes. The inclination angle and three-dimensional velocity of the largest jet were inferred from the imaging and spectroscopic observations, which show a high consistence with those derived from the stereoscopic analysis using dual-perspective observations by {it SDO}/AIA and {it STEREO}-B/EUVI. By relating the jets to the local UV/EUV and full-disk {it GOES} X-ray emission enhancements, we found that the previous five small-scale jets were triggered by five bright points while the last/largest one was triggered by a C1.6 solar flare. Together with a number of type III radio bursts generated during the jet eruptions as well as a weak CME that was observed in association with the last jet, our observations provide evidences in support of multi-scale magnetic reconnection processes being responsible for the production of jet events.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
