اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدملاحظات الطيف البصري للمؤشر المتوسط EX Hydrae في الإستقرار
Spectroscopic Observations of the Intermediate Polar EX Hydrae in Quiescence
335
0
0.0
(
0
)
اسأل ChatGPT حول البحث
نقدم هنا نتائج الملاحظات الطيفية للموجب المتوسط (IP) EX Hya في الإستقرار خلال عامي 1991 و 2001. تم الكشف عن سرعات نحوية معدلة بالدوران تتوافق مع مصدر قرص خارجي لأول مرة في IP. تم تعديل الدوران الإشعاعي مع سرعات تقريبا بالقرب من ~500-600 كم / س. هذه السرعات تتوافق مع تلك المواد التي تدور عند حافة القرص المؤخرج، مما يشير إلى تطابق الدوران مع الستار المؤخرج في مسافة بالقرب من حجم روش. بالإضافة إلى ذلك، أظهرت رسوم التوموغرام الدوبلر الدورانية دليلاً على وجود إشعاع الستار المؤخرج الذي يمتد من سرعات تقريبا ~500 كم / س إلى ~1000 كم / س. هذه النتائج أكدت النماذج النظرية التي تنبأت بها King & Wynn (1999)، Belle et al. (2002) و Norton et al. (2004) ل EX Hya، التي تنبأ بوجود ستارات مؤخرج كبيرة تمتد إلى مسافة بالقرب من حجم روش في هذا النظام. تم الكشف عن دليل على وجود جريان تجاوز يسقط على المغناطيسية، مؤكداً نتيجة Belle et al. (2005) بأن التجاوز القرص في EX Hya موجود أثناء الإستقرار والإخراج. يبدو أن سرعات الدوران النحوية لهبتا وهجاما ناتجة عن دوران القمع في حافة القرص الخارجية، في حين أن سرعات الهالفا ناتجة عن تدفق المواد على أسطح الأساليب المغناطيسية بعيداً عن الأسد البيضاء (المكون الضيق) وقريباً من الأسد البيضاء (المكون القاعدي الواسع)، موافقاً لنموذج الستار المؤخرج.
Results from spectroscopic observations of the Intermediate Polar (IP) EX Hya in quiescence during 1991 and 2001 are presented. Spin-modulated radial velocities consistent with an outer disc origin were detected for the first time in an IP. The spin pulsation was modulated with velocities near ~500-600 km/s. These velocities are consistent with those of material circulating at the outer edge of the accretion disc, suggesting corotation of the accretion curtain with material near the Roche lobe radius. Furthermore, spin Doppler tomograms have revealed evidence of the accretion curtain emission extending from velocities of ~500 km/s to ~1000 km/s. These findings have confirmed the theoretical model predictions of King & Wynn (1999), Belle et al. (2002) and Norton et al. (2004) for EX Hya, which predict large accretion curtains that extend to a distance close to the Roche lobe radius in this system. Evidence for overflow stream of material falling onto the magnetosphere was observed, confirming the result of Belle et al. (2005) that disc overflow in EX Hya is present during quiescence as well as outburst. It appears that the hbeta and hgamma spin radial velocities originated from the rotation of the funnel at the outer disc edge, while those of halpha were produced due to the flow of material along the field lines far from the white dwarf (narrow component) and close to the white dwarf (broad-base component), in agreement with the accretion curtain model.
قيم البحث
اقرأ أيضاً
We use the best available X-ray data from the intermediate polar EX Hydrae to study the cooling-flow model often applied to interpret the X-ray spectra of these accreting magnetic white dwarf binaries. First, we resolve a long-standing discrepancy be
tween the X-ray and optical determinations of the mass of the white dwarf in EX Hya by applying new models of the inner disk truncation radius. Our fits to the X-ray spectrum now agree with the white dwarf mass of 0.79 M$_{odot}$sun determined using dynamical methods through spectroscopic observations of the secondary. We use a simple isobaric cooling flow model to derive the emission line fluxes, emission measure distribution, and H-like to He-like line ratios for comparison with the 496 ks Chandra High Energy Transmission Grating observation of EX Hydrae. We find that the H/He ratios are not well reproduced by this simple isobaric cooling flow model and show that while H-like line fluxes can be accurately predicted, fluxes of lower-Z He-like lines are significantly underestimated. This discrepancy suggests that some extra heating mechanism plays an important role at the base of the accretion column, where cooler ions form. We thus explored more complex cooling models including the change of gravitational potential with height in the accretion column and a magnetic dipole geometry. None of these modifications to the standard cooling flow model are able to reproduce the observed line ratios. While a cooling flow model with subsolar (0.1 $odot$) abundances is able to reproduce the line ratios by reducing the cooling rate at temperatures lower than $sim 10^{7.3}$ K, the predicted line-to-continuum ratios are much lower than observed. We discuss and discard mechanisms such as photoionization, departures from constant pressure, resonant scattering, different electron-ion temperatures, and Compton cooling. [Abridged]
EX Hya is one of the few double-lined eclipsing cataclysmic variables that allow an accurate measurement of the binary masses. We analyze orbital phase-resolved UVES/ VLT high resolution spectroscopic observations of EX Hya with the aims of deriving
the binary masses and obtaining a tomographic image of the illuminated secondary star. We present a novel method for determining the binary parameters by directly fitting an emission model of the illuminated secondary star to the phase-resolved line profiles of NaI lambda 8183/ 8195 in absorption and emission and CaII lambda 8498 in emission. The fit to the NaI and CaII line profiles, combined with the published K1, yields a white-dwarf mass M1 = 0.790 +/- 0.026 Msun, a secondary mass M2 = 0.108 +/- 0.008 Msun, and a velocity amplitude of the secondary star K2 = 432.4 +/- 4.8 km s-1. The secondary is of spectral type dM5.5 +/- 0.5 and has an absolute K-band magnitude of MK = 8.8. Its Roche radius places it on or very close to the main sequence of low-mass stars. It differs from a main sequence star by its illuminated hemisphere that faces the white dwarf. The secondary star contributes only 5% to the observed spin-phase averaged flux at 7500 A, 7.5% at 8200 A, and 37% in the K-band. We present images of the secondary star in the light of the NaI doublet and the CaII emission line derived with a simplified version of Roche tomography. We have discovered narrow spectral lines from the secondary star in EX Hya that delineate its orbital motion and allow us to derive accurate masses of both components. The primary mass significantly exceeds recently published values. The secondary is a low-mass main sequence star that displays a rich emission line spectrum on its illuminated side, but lacks chromospheric emission on its dark side.
In magnetically accreting white dwarfs, the height above the white dwarf surface where the standing shock is formed is intimately related with the accretion rate and the white dwarf mass. However, it is difficult to measure. We obtained new data with
NuSTAR and Swift that, together with archival Chandra data, allow us to constrain the height of the shock in the intermediate polar EX Hya. We conclude that the shock has to form at least at a distance of about one white dwarf radius from the surface in order to explain the weak Fe K{alpha} 6.4 keV line, the absence of a reflection hump in the high-energy continuum, and the energy dependence of the white dwarf spin pulsed fraction. Additionally, the NuSTAR data allowed us to measure the true, uncontaminated hard X-ray (12-40 keV) flux, whose measurement was contaminated by the nearby galaxy cluster Abell 3528 in non-imaging X-ray instruments.
We present the first results from a long (496 ks) Chandra High Energy Transmission Grating observation of the intermediate polar EX Hydrae. In addition to the narrow emission lines from the cooling post-shock gas, for the first time we have detected
a broad component in some of the X-ray emission lines, namely O VIII 18.97, Mg XII 8.42, Si XIV 6.18, and Fe XVII 16.78. The broad and narrow components have widths of ~ 1600 km s^-1 and ~ 150 km s^-1, respectively. We propose a scenario where the broad component is formed in the pre-shock accretion flow, photoionized by radiation from the post-shock flow. Because the photoionized region has to be close to the radiation source in order to produce strong photoionized emission lines from ions like O VIII, Fe XVII, Mg XII, and Si XIV, our photoionization model constrains the height of the standing shock above the white dwarf surface. Thus, the X-ray spectrum from EX Hya manifests features of both magnetic and non-magnetic cataclysmic variables.
We present photometry of the intermediate polar FO Aquarii obtained as part of the K2 mission using the Kepler space telescope. The amplitude spectrum of the data confirms the orbital period of 4.8508(4) h, and the shape of the light curve is consist
ent with the outer edge of the accretion disk being eclipsed when folded on this period. The average flux of FO Aquarii changed during the observations, suggesting a change in the mass accretion rate. There is no evidence in the amplitude spectrum of a longer period that would suggest disk precession. The amplitude spectrum also shows the white dwarf spin period of 1254.3401(4) s, the beat period of 1351.329(2) s, and 31 other spin and orbital harmonics. The detected period is longer than the last reported period of 1254.284(16) s, suggesting that FO Aqr is now spinning down, and has a positive $dot{P}$. There is no detectable variation in the spin period over the course of the K2 observations, but the phase of the spin cycle is correlated with the system brightness. We also find the amplitude of the beat signal is correlated with the system brightness.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
