भारतीय खगोलभौतिकी संस्थान
Indian Institute of Astrophysics
Exploring the Universe since 1786

We present ionization structures of IC 2003, a planetary nebula with [WR] central star, using a 1-D dusty photo-ionization code: ”CLOUDY 17.03”. The photo-ionization model is constrained by archival UV emission line fluxes, medium-resolution optical spectroscopy, IRAS 25 µm flux, absolute Hβ flux, and the mean angular size of the nearly spherical optical nebula. To constrain the carbon abundance and the effect of photo-electric heating in the ionized gas, we used UV emission lines. We considered an amorphous carbon dust grain with MRN and KMH size distributions to address the importance of photo-electric heating in the ionized nebula. We show that KMH grain size distribution with quantum dust heating reproduces the observations quite well. We construct the ionization structures of different elements at their different ionization stages in the nebula. We derive the physical properties of the planetary nebula and its chemical composition, as well as the parameters of its central star. The estimated nebular dust-to-gas mass ratio is 2:37 x 103 , and the enhanced photo-electric heating yielded by small dust grains is 9:4% of the total heating. We considered the H-poor model atmosphere for the central star; the effective temperature of the central star is 177 kK, the specific gravity log(g) is 6, and its luminosity (L*) is 6425 Lʘ. The derived central star parameters plotted on stellar evolutionary tracks correspond to a central star mass of 0.636 Mʘ and to a progenitor mass of 3.26 Mʘ.

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We carried out the first high-resolution transit observations of the exoplanet WASP-49 Ab with Keck/HIRES. Upon custom wavelength calibration we achieve a Doppler RV precision of < 60 ms−1 . This is an improvement in RV stability of roughly 240 ms−1 with respect to the instrument standard. We report an average sodium flux residual of ΔFNaD/F⋆(λ)∼ 3.2 ± 0.4 per cent (8.0 σ ) comparable to previous studies. Interestingly, an average Doppler shift of ‑6.2 ± 0.5 kms−1 (12.4 σ ) is identified offset from the exoplanet rest frame. The velocity residuals in time trace a blueshift (v Γ,ingress∼ ‑10.3 ± 1.9 kms−1 ) to redshift (v Γ,egress∼ + 4.1 ± 1.5 kms−1 ), suggesting the origin of the observed sodium is unlikely from the atmosphere of the planet. The average Na light curves indicate a depth of ΔFNaD/F⋆(t)∼ 0.47 ± 0.04 per cent (11.7 σ ) enduring ≲ 90 min with a half-max duration of ∼ 40.1 min. Frequent high-resolution spectroscopic observations will be able to characterize the periodicity of the observed Doppler shifts. Considering the origin of the transient sodium gas is of unknown geometry, a co-orbiting natural satellite may be a likely source.

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Small-scale brightenings (SBs) are commonly observed in the transition region (TR) that separates the solar chromosphere from the corona. These brightenings, omnipresent in active region patches known as "moss" regions, could potentially contribute to the heating of active region plasma. In this study, we investigate the properties of SB events in a moss region and their associated chromospheric dynamics, which could provide insights into the underlying generation mechanisms of the SBs. We analyzed the data sets obtained by coordinated observations using the Interface Region Imaging Spectrograph and the Goode Solar Telescope at Big Bear Solar Observatory. We studied 131 SB events in our region of interest and found that 100 showed spatial and temporal matches with the dynamics observed in the chromospheric Hα images. Among these SBs, 98 of them were associated with spicules that are observed in Hα images. Furthermore, detailed analysis revealed that one intense SB event corresponded to an Ellerman bomb (EB), while another SB event consisted of several recurring brightenings caused by a stream of falling plasma. We observed that Hα far wings often showed flashes of strong brightening caused by the falling plasma, creating an Hα spectral profile similar to an EB. However, 31 of the 131 investigated SB events showed no noticeable spatial and temporal matches with any apparent features in Hα images. Our analysis indicated that the predominant TR SB events in moss regions are associated with chromospheric phenomena primarily caused by spicules. Most of these spicules display properties akin to dynamic fibrils.

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