اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEffects of the chromospheric Ly{alpha} line profile shape on the determination of the solar wind HI outflow velocity using the Doppler dimming technique
67
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The determination of solar wind outflow velocity is fundamental in order to probe the mechanisms of wind acceleration in the corona. We aim to study, via the Doppler dimming technique, the effects that the chromospheric Ly{alpha} line profile shape causes on the determination of the outflow speed of coronal HI atoms. The Doppler dimming technique takes into account the decrease of coronal Ly{alpha} radiation in regions where HI atoms flow out in the solar wind. Starting from UV observations (UVCS/SOHO) of the coronal Ly{alpha} line and simultaneous measurements of pB (LASCO/SOHO and Mk3/MLSO), we studied the effect of the pumping chromospheric Ly{alpha} line profile through measurements from SOHO/SUMER, UVSP/SMM and LPSP/OSO-8, taken from representative on-disk regions and as a function of time during the solar activity cycle. In particular, we considered the effect of four chromospheric line parameters: line width, depth of the central reversal, asymmetry and distance of the peaks. We find that the range of variability of these parameters is of about 50% for the width, 69% for the depth of the central reversal, 35% for the asymmetry, and 50% for the distance of the peaks. Then, we find that the variability of the pumping Ly{alpha} profile affects the estimates of the coronal HI velocity by about 9-12%. Therefore, this uncertainty is smaller than other physical quantities uncertainties, and a constant in time and unique shape of the Ly{alpha} profile over the solar disk can be adopted in order to estimate the solar wind outflow velocity.
قيم البحث
اقرأ أيضاً
The asymmetries observed in the line profiles of solar flares can provide important diagnostics of the properties and dynamics of the flaring atmosphere. In this paper the evolution of the Halpha and Ca II 8542 {AA} lines are studied using high spati
al, temporal and spectral resolution ground-based observations of an M1.1 flare obtained with the Swedish 1-m Solar Telescope. The temporal evolution of the Halpha line profiles from the flare kernel shows excess emission in the red wing (red asymmetry) before flare maximum, and excess in the blue wing (blue asymmetry) after maximum. However, the Ca II 8542 {AA} line does not follow the same pattern, showing only a weak red asymmetry during the flare. RADYN simulations are used to synthesise spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. We show that the red asymmetry observed in Halpha is not necessarily associated with plasma downflows, and the blue asymmetry may not be related to plasma upflows. Indeed, we conclude that the steep velocity gradients in the flaring chromosphere modifies the wavelength of the central reversal in the Halpha line profile. The shift in the wavelength of maximum opacity to shorter and longer wavelengths generates the red and blue asymmetries, respectively.
Recent studies of interstellar neutral (ISN) hydrogen observed by the Interstellar Boundary Explorer (IBEX) suggested that the present understanding of the radiation pressure acting on hydrogen atoms in the heliosphere should be revised. There is a s
ignificant discrepancy between theoretical predictions of the ISN H signal using the currently used model of the solar Lyman-alpha profile by Tarnopolski et al. 2009 (TB09) and the signal due to ISN H observed by IBEX-Lo. We developed a new model of evolution of the solar Lyman-alpha profile that takes into account all available observations of the full-disk solar Lyman-alpha profiles from SUMER/SOHO, provided by Lemaire et al. 2015 (L15), covering practically the entire 23rd solar cycle. The model has three components that reproduce different features of the profile. The main shape of the emission line that is produced in the chromosphere is modeled by the kappa function; the central reversal due to absorption in the transition region is modeled by the Gauss function; the spectral background is represented by the linear function. The coefficients of all those components are linear functions of the line-integrated full-disk Lyman-alpha irradiance, which is the only free parameter of the model. The new model features potentially important differences in comparison with the model by TB09, which was based on a limited set of observations. This change in the understanding of radiation pressure, especially during low solar activity, may significantly affect the interstellar H and D distributions in the inner heliosphere and their derivative populations.
We present a modification of a model of solar cycle evolution of the solar Lyman-alpha line profile, along with a sensitivity study of interstellar neutral H hydrogen to uncertainties in radiation pressure level. The line profile model, originally de
veloped by Kowalska-Leszczynska et al. 2018a, is parametrized by the composite solar Lyman-alpha flux, which recently was revised Machol et al. 2019. We present modified parameters of the previously-developed model of solar radiation pressure for neutral hydrogen and deuterium atoms in the heliosphere. The mathematical function used in the model, as well as the fitting procedure, remain unchanged. We show selected effects of the model modification on ISN H properties in the heliosphere and we discuss the sensitivity of these quantities to uncertainties in the calibration of the composite Lyman-alpha series.
We use 3D hydrodynamics simulations followed by synthetic line profile calculations to examine the effect increasing the strength of the stellar wind has on observed Ly-$alpha$ transits of a Hot Jupiter (HJ) and a Warm Neptune (WN). We find that incr
easing the stellar wind mass-loss rate from 0 (no wind) to 100 times the solar mass-loss rate value causes reduced atmospheric escape in both planets (a reduction of 65% and 40% for the HJ and WN, respectively, compared to the no wind case). For weaker stellar winds (lower ram pressure), the reduction in planetary escape rate is very small. However, as the stellar wind becomes stronger, the interaction happens deeper in the planetary atmosphere and, once this interaction occurs below the sonic surface of the planetary outflow, further reduction in evaporation rates is seen. We classify these regimes in terms of the geometry of the planetary sonic surface. Closed refers to scenarios where the sonic surface is undisturbed, while open refers to those where the surface is disrupted. We find that the change in stellar wind strength affects the Ly-$alpha$ transit in a non-linear way. Although little change is seen in planetary escape rates ($simeq 5.5times 10^{11}$g/s) in the closed to partially open regimes, the Ly-$alpha$ absorption (sum of the blue [-300, -40 km/s] & red [40, 300 km/s] wings) changes from 21% to 6% as the stellar wind mass-loss rate is increased in the HJ set of simulations. For the WN simulations, escape rates of $simeq 6.5times 10^{10}$g/s can cause transit absorptions that vary from 8.8% to 3.7%, depending on the stellar wind strength. We conclude that the same atmospheric escape rate can produce a range of absorptions depending on the stellar wind and that neglecting this in the interpretation of Ly-$alpha$ transits can lead to underestimation of planetary escape rates.
Following the derivation of a more accurate model of the evolution of the solar Lyman-$alpha$ line with the changing solar activity by Kowalska-leszczynska et al. 2018 (IKL18) than the formerly used model by Tarnopolski et al. 2009 (ST09), we investi
gate potential consequences that adoption of the resulting refined model of radiation pressure has for the model distribution of interstellar neutral (ISN) H in the inner heliosphere and on the interpretation of selected observations. We simulated the ISN H densities using the two alternative radiation pressure models and identical models of all other factors affecting the ISN H distribution. We found that during most of the solar cycle, the IKL18 model predicts larger densities of ISN H and PUIs than ST09 in the inner heliosphere, especially in the downwind hemisphere. However, the density of ISN H at the termination shock estimated by Bzowski et al. 2008 obtained using ST09 does not need revision, and the detection of ISN D by IBEX is supported. However, we point out the existence of a considerable absorption of a portion of the solar Lyman-$alpha$ spectral flux inside the heliosphere. Therefore, the model of radiation pressure for ISN H is still likely to need revision, and hence the available models of ISN H are not self-consistent.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
