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Register a new userTemplate RR Lyrae H alpha, H beta, and H gamma Velocity Curves
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Authors
Branimir Sesar
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We present template radial velocity curves of $ab$-type RR Lyrae stars constructed from high-precision measurements of ${rm Halpha}$, ${rm Hbeta}$, and ${rm Hgamma}$ lines. Amplitude correlations between the Balmer line velocity curves, Johnson $V$-band, and SDSS $g$- and $r$-band light curves are also derived. Compared to previous methods, these templates and derived correlations reduce the uncertainty in measured systemic (center-of-mass) velocities of RR Lyrae stars by up to 15 {kms}, and will be of particular interest to wide-area spectroscopic surveys such as the Sloan Digital Sky Survey (SDSS) and LAMOST Experiment for Galactic Understanding and Exploration (LEGUE).
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We present new H$alpha$ and H$beta$ images of the HH~1/2 system, and we find that the H$alpha$/H$beta$ ratio has high values in ridges along the leading edges of the HH~1 bow shock and of the brighter condensations of HH~2. These ridges have H$alpha$/H$beta=4to 6$, which is consistent with collisional excitation from the $n=1$ to the $n=3$ and 4 levels of hydrogen in a gas of temperatures $T=1.5to 10times 10^4$~K. This is therefore the first direct proof that the collisional excitation/ionization region of hydrogen right behind Herbig-Haro shock fronts is detected.
The so-called H$alpha$ third emission occurs around pulsation phase $varphi$=0.30. It has been observed for the first time in 2011 in some RR Lyrae stars. The emission intensity is very weak, and its profile is a tiny persistent hump in the red side-line profile. We report the first observation of the H$alpha$ third emission in RR Lyr itself (HD 182989), the brightest RR Lyrae star in the sky. New spectra were collected in 2013-2014 with the Aurelie}spectrograph (resolving power R=22$,$700, T152, Observatoire de Haute-Provence, France) and in 2016-2017 with the eShel spectrograph (R=11$,$000, T035, Observatoire de Chelles, France). In addition, observations obtained in 1997 with the Elodie spectrograph (R=42$,$000, T193, Observatoire de Haute-Provence, France) were reanalyzed. The H$alpha$ third emission is clearly detected in the pulsation phase interval $varphi$=0.188-0.407, that is, during about 20% of the period. Its maximum flux with respect to the continuum is about 13%. The presence of this third emission and its strength both seem to depend only marginally on the Blazhko phase. The physical origin of the emission is probably due to the infalling motion of the highest atmospheric layers, which compresses and heats the gas that is located immediately above the rising shock wave. The infalling velocity of the hot compressed region is supersonic, almost 50 km$cdot$s$^{-1}$, while the shock velocity may be much lower in these pulsation phases. When the H$alpha$ third emission appears, the shock is certainly no longer radiative because its intensity is not sufficient to produce a blueshifted emission component within the H$alpha$ profile. At phase $varphi$=0.40, the shock wave is certainly close to its complete dissipation in the atmosphere.
We present new {it Hubble Space Telescope} images of high-velocity H-$alpha$ and Lyman-$alpha$ emission in the outer debris of SN~1987A. The H-$alpha$ images are dominated by emission from hydrogen atoms crossing the reverse shock. For the first time we observe emission from the reverse shock surface well above and below the equatorial ring, suggesting a bipolar or conical structure perpendicular to the ring plane. Using the H$alpha$ imaging, we measure the mass flux of hydrogen atoms crossing the reverse shock front, in the velocity intervals ($-$7,500~$<$~$V_{obs}$~$<$~$-$2,800 km s$^{-1}$) and (1,000~$<$~$V_{obs}$~$<$~7,500 km s$^{-1}$), $dot{M_{H}}$ = 1.2~$times$~10$^{-3}$ M$_{odot}$ yr$^{-1}$. We also present the first Lyman-$alpha$ imaging of the whole remnant and new $Chandra$ X-ray observations. Comparing the spatial distribution of the Lyman-$alpha$ and X-ray emission, we observe that the majority of the high-velocity Lyman-$alpha$ emission originates interior to the equatorial ring. The observed Lyman-$alpha$/H-$alpha$ photon ratio, $langle$$R(Lalpha / Halpha)$$rangle$ $approx$~17, is significantly higher than the theoretically predicted ratio of $approx$ 5 for neutral atoms crossing the reverse shock front. We attribute this excess to Lyman-$alpha$ emission produced by X-ray heating of the outer debris. The spatial orientation of the Lyman-$alpha$ and X-ray emission suggests that X-ray heating of the outer debris is the dominant Lyman-$alpha$ production mechanism in SN 1987A at this phase in its evolution.
Symbiotic stars often exhibit broad wings around Balmer emission lines, whose origin is still controversial. We present the high resolution spectra of the S type symbiotic stars Z Andromedae and AG Draconis obtained with the ESPaDOnS and the 3.6 m Canada France Hawaii Telescope to investigate the broad wings around H$alpha$ and H$beta$. When H$alpha$ and H$beta$ lines are overplotted in the Doppler space, it is noted that H$alpha$ profiles are overall broader than H$beta$ in these two objects. Adopting a Monte Carlo approach, we consider the formation of broad wings of H$alpha$ and H$beta$ through Raman scattering of far UV radiation around Ly$beta$ and Ly$gamma$ and Thomson scattering by free electrons. Raman scattering wings are simulated by choosing an H I region with a neutral hydrogen column density $N_{HI}$ and a covering factor $CF$. For Thomson wings, the ionized scattering region is assumed to cover fully the Balmer emission nebula and is characterized by the electron temperature $T_e$ and the electron column density $N_e$. Thomson wings of H$alpha$ and H$beta$ have the same width that is proportional to $T_e^{1/2}$. However, Raman wings of H$alpha$ are overall three times wider than H$beta$ counterparts, which is attributed to different cross section for Ly$beta$ and Ly$gamma$. Normalized to have the same peak values and presented in the Doppler factor space. H$alpha$ wings of Z And and AG Dra are observed to be significantly wider than H$beta$ counterpart, favoring the Raman scattering origin of broad Balmer wings.
Deuterated molecules are important chemical tracers of prestellar and protostellar cores. Up to now, the titular reaction has been assumed to contribute to the generation of these deuterated molecules. We have measured the merged-beams rate coefficient for this reaction as function of the relative collision energy in the range of about 10 meV to 10 eV. By varying the internal temperature of the reacting H$_3^+$ molecules, we found indications for the existence of a reaction barrier. We have performed detailed theoretical calculations for the zero-point-corrected energy profile of the reaction and determined a new value for the barrier height of $approx$ 68 meV. Furthermore, we have calculated the tunneling probability through the barrier. Our experimental and theoretical results show that the reaction is essentially closed at astrochemically relevant temperatures. We derive a thermal rate coefficient of $<1times 10^{-12}$ cm$^3$ s$^{-1}$ for temperatures below 75 K with tunneling effects included and below 155 K without tunneling.
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