Related papers: A physically motivated `charge-exchange method' fo…
We investigate the electron temperature gradient in the galactic disk as measured by young HII regions on the basis of radio recombination lines and the corresponding gradient in planetary nebulae (PN) based on [OIII] electron temperatures.…
In an attempt to remove the systematic errors which have plagued the calibration of the HII region abundance sequence, we have theoretically modeled the extragalactic HII region sequence. We then used the theoretical spectra so generated in…
Three Galactic HII regions, viz., S 201, S 206, and S 209 have been imaged at three frequencies, viz., 232, 327, and 610 MHz using the GMRT. The resolutions of these images are typically 15" at 232, 10" at 327, and 6" at 610 MHz. These are…
We present spectroscopic observations of a sample of 72 emission-line objects, including mainly HII regions, in the spiral galaxy M 33. Spectra were obtained with the multi-object, wide field spectrograph AF2/WYFFOS at the 4.2m WHT…
There is evidence for temperature fluctuations in Planetary Nebulae and in Galactic HII regions. If such fluctuations occur in the low-metallicity, extragalactic HII regions used to probe the primordial helium abundance, the derived 4He…
The [NII] 122 and 205 \mu m transitions are powerful tracers of the ionized gas in the interstellar medium. By combining data from 21 galaxies selected from the Herschel KINGFISH and Beyond the Peak surveys, we have compiled 141 spatially…
Using ab-initio photoionization models of giant HII regions, we test methods for abundance determinations based on a direct measurement of the electron temperature, now possible even for moderate to high-metallicity objects. We find that,…
In non-star-forming, passively evolving galaxies, regions with emission lines dominated by low-ionization species are classified as Low-Ionization Emission Regions (LIERs). The ionization mechanism behind such regions has long been a…
It has been proposed that the charge exchange (CX) process at the interface between hot and cool interstellar gases could contribute significantly to the observed soft X-ray emission in star forming galaxies. We analyze the XMM-Newton/RGS…
We analyze high signal-to-noise spectrophotometric observations acquired simultaneously with TWIN, a double-arm spectrograph, from 3400 to 10400 \AA of three star-forming regions in the HII galaxy SDSS J165712.75+321141.4. We have measured…
We have constructed photo-ionization models of five galactic bulge planetary nebulae using our automatic method which enables a fully self-consistent determination of the physical parameters of a planetary nebula. The models are constrained…
The temperatures of the heavy ions ($T_i$) in the solar corona provide critical information about the heating mechanism of the million-degree corona. However, the measurement of $T_i$ is usually challenging due to the nonthermal motion,…
We present long slit spectrophotometry of two HII regions: TOL2146-391 and TOL0357-3915. We performed a detailed analysis that involves abundance determinations relaxing the assumption of homogeneous temperature. The temperature…
We present an observational study about the impacts of the interactions in the electron density of \ion{H}{ii} regions located in 7 systems of interacting galaxies. The data consist of long-slit spectra in the range 4400-7300 A, obtained…
In this work, we present a new catalogue of >40000 ionised nebulae distributed across the 19 galaxies observed by the PHANGS-MUSE survey. The nebulae have been classified using a new model-comparison-based algorithm that exploits the odds…
We use a sample of 154 observations of 124 H II regions that have measurements of both Te[O III] and Te[N II], compiled from the literature, to explore the behaviour of the Te[O III]-Te[N II] temperature relation. We confirm that the…
While collisionally excited lines in HII regions allow one to easily probe the chemical composition of the interstellar medium in galaxies, the possible presence of important temperature fluctuations casts some doubt on the derived…
A recently generated theoretical line list of C II dielectronic recombination lines together with observational data gathered from the literature is used to investigate the electron temperature in a range of astronomical objects, mainly…
Connecting the gas in HII regions to the underlying source of the ionizing radiation can help us constrain the physical processes of stellar feedback and how HII regions evolve over time. With PHANGS$\unicode{x2013}$MUSE we detect nearly…
We study the sensitivity of the methods available for abundance determinations in H II regions to potential observational problems. We compare the dispersions they introduce around the oxygen and nitrogen abundance gradients when applied to…