Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSignatures of quiet Sun reconnection events in Ca~{sc ii}, H$alpha$ and Fe~{sc i}
293
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We use observations of quiet Sun (QS) regions in the H$alpha$ 6563 AA, Ca~{sc ii} 8542 AA, and Fe~{sc i} 6302 AA lines. We observe brightenings in the wings of the H$alpha$ and Ca~{sc ii} combined with observations of the interacting magnetic concentrations observed in the Stokes signals of Fe~{sc i}. These brightenings are similar to Ellerman bombs (EBs), i.e. impulsive bursts in the wings of the Balmer lines which leave the line cores unaffected. Such enhancements suggest that these events have similar formation mechanisms to the classical EBs found in active regions, with the reduced intensity enhancements found in the QS regions due to a weaker feeding magnetic flux. The observations also show that the quiet Sun Ellerman bombs (QSEBs) are formed at a higher height in the upper photosphere than the photospheric continuum level. Using simulations, we investigate the formation mechanism associated with the events and suggest that these events are driven by the interaction of magnetic field-lines in the upper photospheric regions. The results of the simulation are in agreement with observations when comparing the light-curves, and in most cases we found that the peak in the Ca~{sc ii} 8542 AA wing occurred before the peak in H$alpha$ wing. Moreover, in some cases, the line profiles observed in Ca~{sc ii} are asymmetrical with a raised core profile. The source of heating in these events is shown by the MURaM simulations and is suggested to occur 430 km above the photosphere.
rate research
Read More
We present a near infrared study of the stellar content of 35 H,{sc{ii}} regions in the Galactic plane. In this work, we have used the near infrared domain $J-$, $H-$ and $K_{s}-$ band color images to visually inspect the sample. Also, color-color and color-magnitude diagrams were used to indicate ionizing star candidates, as well as, the presence of young stellar objects such as classical TTauri Stars (CTTS) and massive young stellar objects (MYSOs). We have obtained {it Spitzer} IRAC images for each region to help further characterize them. {it Spitzer} and near infrared morphology to place each cluster in an evolutionary phase of development. {it Spitzer} photometry was also used to classify the MYSOs. Comparison of the main sequence in color-magnitude diagrams to each observed cluster was used to infer whether or not the cluster kinematic distance is consistent with brightnesses of the stellar sources. We find qualitative agreement for a dozen of the regions, but about half the regions have near infrared photometry that suggests they may be closer than the kinematic distance. A significant fraction of these already have spectrophotometric parallaxes which support smaller distances. These discrepancies between kinematic and spectrophotometric distances are not due to the spectrophotometric methodologies, since independent non-kinematic measurements are in agreement with the spectrophotometric results. For instance, trigonometric parallaxes of star-forming regions were collected from the literature and show the same effect of smaller distances when compared to the kinematic results. In our sample of H,{sc{ii}} regions, most of the clusters are evident in the near infrared images. Finally, it is possible to distinguish among qualitative evolutionary stages for these objects.
Interpreting the Stokes profiles observed in quiet regions of the solar chromosphere is a challenging task. The Stokes Q and U profiles are dominated by the scattering polarisation and the Hanle effect, and these processes can only be correctly quantified if 3D radiative transfer effects are taken into account. Forward-modelling of the intensity and polarisation of spectral lines using a 3D model atmosphere is a suitable approach in order to statistically compare the theoretical and observed line profiles. Our aim is to present novel observations of the Ca 8542 line profiles in a quiet region at the centre of the solar disc and to quantitatively compare them with the theoretical Stokes profiles. We aim at estimating the reliability of the 3D model atmosphere using not only the line intensity but the full vector of Stokes parameters. We used data obtained with the ZIMPOL instrument at the IRSOL and compared the observations with the theoretical profiles computed with the PORTA radiative transfer code, using as solar model atmosphere a 3D snapshot taken from a radiation-magnetohydrodynamics simulation. The synthetic profiles were degraded to match the instrument and observing conditions. The degraded theoretical profiles of the Ca 8542 line are qualitatively similar to the observed ones. We confirm that there is a fundamental difference in the widths of all Stokes profiles: the observed lines are wider than the theoretical lines. We find that the amplitudes of the observed profiles are larger than those of the theoretical ones, which suggests that the symmetry breaking effects in the solar chromosphere are stronger than in the model atmosphere. This means that the isosurfaces of temperature, velocity, and magnetic field strength and orientation are more corrugated in the solar chromosphere than in the currently available 3D radiation-magnetohydrodynamics simulation.
We report the observational findings of the Sh2-112 H{sc ii} region by using the multiwavelength data analysis ranging from optical to radio wavelengths. This region is powered by a massive O8V-type star BD +45 3216. The surface density distribution and minimum spanning tree analyses of the young stellar object (YSO) candidates in the region reveal their groupings toward the western periphery of the H{sc ii} region. A GMRT radio continuum emission peak is found toward the north-west boundary of the H{sc ii} region and is investigated as a compact/ultra-compact H{sc ii} region candidate powered by a B0-B0.5 type star. Toward the south-west direction, a prominent curved rim-like structure is found in the H$alpha$ image and GMRT radio continuum maps, where the H$_2$ and $^{13}$CO emission is also observed. These results suggest the existence of the ionized boundary layer (IBL) on the surface of the molecular cloud. This IBL is found to be over-pressurized with respect to the internal pressure of the surrounding molecular cloud. This implies that the shocks are propagating/ propagated into the molecular cloud and the young stars identified within it are likely triggered due to the massive star. It is also found that this region is ionization bounded toward the west-direction and density bounded toward the east-direction. Based on the distribution of the ionized gas, molecular material, and the YSO candidates; we propose that the Sh2-112 H{sc ii} region is a good candidate for the blister-type H{sc ii} region which has been evolved on the surface of a cylindrical molecular cloud.
Solar spicules are chromospheric fibrils that appear everywhere on the Sun, yet their origin is not understood. Using high resolution observations of spicules obtained with the Swedish 1-m Solar Telescope, we aim to understand how spicules appear in filtergrams and Dopplergrams, how they compare in Ca II H and H-alpha, and what can make them appear and disappear. We find thatspicules display a rich and detailed spatial structure, and show a distribution of transverse velocities that when aligned with the line of sight can make them appear at different H-alpha wing positions. They become more abundant at positions closer to the line core, reflecting a distribution of Doppler shifts and widths. In H-alpha width maps they stand out as bright features both on disk and off limb, reflecting their large Doppler motions and possibly higher temperatures than in the typical H-alpha formation region. Spicule lifetimes measured from narrowband images at only a few positions will be an underestimate because Doppler shifts can make them disappear prematurely from such images; for such cases, width maps are a more robust tool. In H-alpha and Ca II H filtergrams, off limb spicules essentially have the same properties, appearance, and evolution. We find that the sudden appearance of spicules can be explained by Doppler shifts from their transverse motions, and does not require other convoluted explanations.
We analyze the high-resolution emission spectrum of WASP-33b taken using the High Dispersion Spectrograph (R,$approx$,165,000) on the 8.2-m Subaru telescope. The data cover $lambda$,$approx$,$6170$-$8817$,AA, divided over 30 spectral orders. The telluric and stellar lines are removed using a de-trending algorithm, {sc SysRem}, before cross-correlating with planetary spectral templates. We calculate the templates assuming a 1-D plane-parallel hydrostatic atmosphere including continuum opacity of bound-free H$^{-}$ and Rayleigh scattering by H$_{2}$ with a range of constant abundances of Fe,{sc i}. Using a likelihood-mapping analysis, we detect an Fe,{sc i} emission signature at 6.4-$sigma$ located at $K_{mathrm{p}}$ of 226.0,$^{+2.1}_{-2.3}$,km,s$^{-1}$and $v_{mathrm{sys}}$ of -3.2,$^{+2.1}_{-1.8}$,km,s$^{-1}$ -- consistent with the planets expected velocity in the literature. We also confirm the existence of a thermal inversion in the day-side of the planet which is very likely to be caused by the presence of Fe,{sc i} and previously-detected TiO in the atmosphere. This makes WASP-33b one of the prime targets to study the relative contributions of both species to the energy budget of an ultra-hot Jupiter.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
