Search Publications
Spectroscopic diagnosis of a B-class flare and an associated filament eruption
Kayshap, Pradeep; Babu, B. Suresh; Tripathi, Sharad C.
The flare ribbon and an associated filament eruption are diagnosed using O IV 1401.16 Å, Si IV 1402.77 Å, and Mg II k 2796.35 Å spectral lines provided by Interface Region Imaging Spectrograph (IRIS). The flare ribbons have downflow (redshifts) in all these lines, and this redshift decreases from the transition region to the chromosphere. While th…
Solar orbiter: a short review of the mission and early science results
Müller, Daniel; Harra, Louise
On 9 February 2020 at 11:03 pm EST, an Atlas V 411 rocket launched the ESA/ NASA Solar Orbiter mission. This mission was the culmination of decades of work across many countries to achieve the goal of getting close to the Sun and measuring how the Sun creates and maintains the heliosphere. The mission's goal is to understand how the inner heliosph…
A study on the evolutionary period changes of short-period type II cepheids
Pastukhova, Elena N.; Yacob, Alemiye Mamo; Berdinkov, Leonid N.
We investigate the period changes of 13 short-period Type II Cepheids using the O-C method over a century-long data baseline. The O-C diagrams for these stars exhibit a parabolic trend, indicating both increasing and decreasing period changes over time. These observed period changes are consistent with recent theoretical models based on horizontal…
Is there a black hole in the center of the Sun?
Bellinger, Earl P.; Caplan, Matthew E.; Santarelli, Andrew D.
There is probably not a black hole in the center of the Sun. Despite this detail, our goal in this work to convince the reader that this question is interesting and that work studying stars with central black holes is well motivated. If primordial black holes exist then they may exist in sufficiently large numbers to explain the dark matter in the…
On the mass assembly history of the Milky Way: clues from its stellar halo
Horta, Danny; Schiavon, Ricardo P.
Stellar halos of galaxies retain crucial clues to their mass assembly history. It is in these galactic components that the remains of cannibalised galactic building blocks are deposited. For the case of the Milky Way, the opportunity to analyse the stellar halo's structure on a star-by-star basis in a multi-faceted approach provides a basis from w…
Galaxy formation catalyzed by gravastars and the JWST, revisited
Adler, Stephen L.
We have proposed that galaxy formation is catalyzed by the collision of infalling and outstreaming particles from leaky, horizonless astrophysical black holes, most likely gravastars, and based on this gave a model for the disk galaxy scale length. In this paper we modify our original scale length formula by including an activation probability
Classification and characterization using HCT/HFOSC spectra of carbon stars selected from the HES survey
Goswami, Aruna; Purandardas, Meenakshi
We present results from the analysis of 88 carbon stars selected from Hamburg/ESO (HES) survey using low-resolution spectra (R ∼1330 & 2190). The spectra were obtained with the Himalayan Faint Object Spectrograph Camera (HFOSC) attached to the 2-m Himalayan Chandra Telescope (HCT). Using well-defined spectral criteria based on the strength of …
Following the tidal trail: a history of modeling the Magellanic Stream
Lucchini, Scott
The formation of the Magellanic Stream has puzzled astronomers for decades. In this review, we outline the history of our understanding of the Magellanic System highlighting key observations that have revolutionized thinking of its evolution. We also walk through the major models and theoretical advances that have led to our current paradigm ‑ (1)…
Self-absorption in solar surge as observed by IRIS
Kayshap, Pradeep; Babu, B. Suresh; Tripathi, Sharad C.
Solar surges are collimated flows of plasma that occur in the periphery of active regions (ARs). The kinematics, physical properties, and triggering mechanisms of a solar surge were studied through imaging and spectroscopic diagnosis. The surge has a typical inverted Y-shape, and it moves with a speed of more than 200 km/s in the transition-region…
A review of 70 years with astrometry: From meridian circles to Gaia and beyond
Høg, Erik
In 1953 I heard of an experiment in 1925 by Bengt Strömgren where he observed transit times with the meridian circle at the Copenhagen University Observatory measuring the current in a photocell behind slits when a star was crossing. In 1954 just 22 years old I was given the task as a student to make first test observations with a new meridian cir…