Related papers: Nonnegative Grassman Chambers are Balls
We have examined star formation in two very luminous (M_V=-22 to -23) Sc-type spiral galaxies, NGC 801 and UGC 2885, using ultra-deep Halpha images. We combine these with UBV and 2MASS JHK images and HI maps to explore the star formation…
Spiral density wave theory attempts to describe the spiral pattern in spiral galaxies in terms of a long-lived wave structure with a constant pattern speed in order to avoid the winding dilemma. The pattern is consequently a rigidly…
We have investigated the infrared properties of a sample of objects with IRAS colors typical of planetary nebulae. The selected objects have not yet evolved to the planetary nebula stage since they have no detectable radio continuum…
In this paper we discuss four early F-type variable stars whose periods are an order of magnitude slower than known pulsators of comparable luminosity. They cannot be stars undergoing simple radial pulsations. For one or more of these stars…
Fireballs are an essential part of any cosmological $\gamma$-ray burst. We drive here a stability criterion for fireballs and show that fireballs are Rayleigh-Taylor unstable in any region in which the entropy decreases outward. The…
Elongated bar-like features are ubiquitous in galaxies, occurring at the centers of approximately two-thirds of spiral disks in the nearby Universe. Due to gravitational interactions between the bar and the other components of galaxies, it…
We generalize the classical notion of packing a set by balls with identical radii to the case where the radii may be different. The largest number of such balls that fit inside the set without overlapping is called its {\em non-uniform…
We estimate a characteristic timescale for star formation in the spiral arms of disk galaxies, going from atomic hydrogen (HI) to dust-enshrouded massive stars. Drawing on high-resolution HI data from The HI Nearby Galaxy Survey and…
Long ($>2$ s) gamma ray bursts (GRBs) are associated with explosions of massive stars, although in three instances, supernovae (SNe) have not been detected, despite deep observations. With new HI line and archival optical integral field…
Radial velocities were measured for 5 potential post-AGB stars, two in the globular cluster NGC 1851 and three in the dSph galaxy Ursa Minor. All five potential PAGB stars were found to be radial velocity non-members.
The inner few hundred parsecs of the Milky Way harbours gas densities, pressures, velocity dispersions, an interstellar radiation field and a cosmic ray ionisation rate orders of magnitude higher than the disc; akin to the environment found…
We have initiated the first CO interferometer survey of early-type spiral galaxies (S0-Sab). We observed five early-type spiral galaxies with HII nuclei (indicating circumnuclear starburst activities). These observations indicate gas masses…
The Cold Neutral Medium (CNM) is an important part of the galactic gas cycle and a precondition for the formation of molecular and star forming gas, yet its distribution is still not fully understood. In this work we present extremely high…
I review the subjects of non-solar cosmic rays (CRs) and long-duration gamma-ray bursts (GRBs). Of the various interpretations of these phenomena, the one best supported by the data is the following. Accreting compact objects, such as black…
Non-rotating neutron stars are generally treated in theoretical studies as perfect spheres. Such a treatment, however, may not be correct if strong magnetic fields are present (such as for magnetars) and/or the pressure of the matter in the…
We identify stellar structures in the PHANGS sample of 74 nearby galaxies and construct morphological masks of sub-galactic environments based on Spitzer 3.6 micron images. At the simplest level, we distinguish centres, bars, spiral arms,…
We have obtained HST_NICMOS images for 72 nearby spiral galaxy bulges in the H-band. These data show that galaxies with regular bulges have steeper nuclear cusps than galaxies with irregular bulges. We also show that galaxies with regular…
It is by now well established that charged rotating Kerr-Newman black holes can support bound-state charged matter configurations which are made of minimally coupled massive scalar fields. We here prove that the externally supported…
The $\gamma$-stable trees are random measured compact metric spaces that appear as the scaling limit of Galton-Watson trees whose offspring distribution lies in a $\gamma$-stable domain, $\gamma \in (1, 2]$. They form a specific class of…
We present experimental measurements on the spontaneous formation of compact spiral structures in vertically-vibrated granular chains. Under weak vibration, when the chain is quasi two-dimensional and self-avoiding, spiral structures emerge…