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Ivan Minchev

Publications and source records attributed to Ivan Minchev.

99 records · Page 6Linked to original sources
arXiv2010

A New Method for Determining the Milky Way Bar Pattern Speed

Previous work has related the Galactic bar to structure in the local stellar velocity distribution. Here we show that the bar also influences the spatial gradients of the velocity vector via the Oort constants. By numerical integration of test-particles we simulate measurements of the Oort C value in a gravitational potential including the Galactic bar. We account for the observed trend that C is increasingly negative for stars with higher velocity dispersion. By comparing measurements of C with our simulations we improve on previous models of the bar, estimating that the bar pattern speed is Omega_b/Omega_0=1.87\pm0.04, where Omega_0 is the local circular frequency, and the bar angle lies within 20[deg]<phi_0<45[deg]. We find that the Galactic bar affects measurements of the Oort constants A and B less than ~2 km/s/kpc for the hot stars.

astro-ph.GA↗
arXiv2009

Radial mixing in the outer Milky Way disk caused by an orbiting satellite

Using test particle simulations we examine the structure of the outer Galactic disk as it is perturbed by a satellite in a tight eccentric orbit about the Galaxy. A satellite of mass a few times 10^9 Msol can heat the outer Galactic disk, excite spiral structure and a warp and induce streams in the velocity distribution. We examine particle eccentricity versus the change in mean radius between initial and current orbits. Correlations between these quantities are reduced after a few satellite pericenter passages. Stars born in the outer galaxy can be moved in radius from their birth positions and be placed in low eccentricity orbits inside their birth radii. We propose that mergers and perturbations from satellite galaxies and subhalos can induce radial mixing in the stellar metallicity distribution.

astro-ph.GA↗
arXiv2008

The Morphology of Collisionless Galactic Rings Exterior to Evolving Bars

The morphology of the outer rings of early-type spiral galaxies is compared to integrations of massless collisionless particles initially in nearly circular orbits. Particles are perturbed by a quadrupolar gravitational potential corresponding to a growing and secularly evolving bar. We find that outer rings with R1R2 morphology and pseudorings are exhibited by the simulations even though they lack gaseous dissipation. Simulations with stronger bars form pseudorings earlier and more quickly than those with weaker bars. We find that the R1 ring, perpendicular to the bar, is fragile and dissolves after a few bar rotation periods if the bar pattern speed increases by more than ~ 8%, bar strength increases (by >~ 140%) after bar growth, or the bar is too strong (Q_T>0.3). If the bar slows down after formation, pseudoring morphology persists and the R2 ring perpendicular to the bar is populated due to resonance capture. The R2 ring remains misaligned with the bar and increases in ellipticity as the bar slows down. The R2 ring becomes scalloped and does not resemble any ringed galaxies if the bar slows down more than 3.5% suggesting that bars decrease in strength before they slow down this much. We compare the morphology of our simulations to B-band images of 9 ringed galaxies from the Ohio State University Bright Spiral Galaxy Survey, and we find a reasonable match in morphologies to R1R2' pseudorings seen within a few bar rotation periods of bar formation. Some of the features previously interpreted in terms of dissipative models may be due to transient structure associated with recent bar growth and evolution.

astro-ph↗
arXiv2005

Twistor and Reflector Spaces of Almost Para-Quaternionic Manifolds

We investigate the integrability of natural almost complex structures on the twistor space of an almost para-quaternionic manifold as well as the integrability of natural almost paracomplex structures on the reflector space of an almost para-quaternionic manifold constructed with the help of a para-quaternionic connection. We show that if there is an integrable structure it is independent on the para-quaternionic connection. In dimension four, we express the anti-self-duality condition in terms of the Riemannian Ricci forms with respect to the associated para-quaternionic structure.

math.DG↗
arXiv2005

Twistors of Almost Quaternionic Manifolds

We investigate the integrability of almost complex structures on the twistor space of an almost quaternionic manifold constructed with the help of a quaternionic connection. We show that if there is an integrable structure it is independent on the quaternionic connection. In dimension four, we express the anti-self-duality condition in terms of the Riemannian Ricci forms with respect to the associated quaternionic structure.

math.DG↗
arXiv2005

Driving spiral arms in the circumstellar disks of HD 100546 and HD 141569A

With 2D hydrodynamical simulations of disks perturbed externally by stars, brown dwarfs or planets we investigate possible scenarios that can account for the spiral structure in circumstellar disks. We consider two scenarios, spiral structure driven by an external bound planet or low mass star and that excited by a previous stellar close encounter or flyby. We find that both scenarios produce morphology similar to that observed in the outer disks of HD 141569A and HD 100546; moderately open 2-armed outer spiral structure. The outer two-armed spiral structure observed in the disk of HD 141569A is qualitatively reproduced with tidal perturbations from its companion binary HD 141569B,C on a prograde orbit near periapse. Our simulation accounts for the outer spiral arms, but is less successful than the secular model of Augereau and Papaloizou at matching the lopsidedness or asymmetry of the disk edge at 300AU. The disk has been previously truncated by the tidal force from the binary. A bound object (stellar or planetary) is unlikely to explain the spiral structure in HD 100546. A co-eval planet or brown dwarf in the disk of sufficient mass to account for the amplitude of the spiral structure would be detectable in NICMOS and STIS images, however existing images reveal no such object. A previous encounter could explain the observed structure, provided that the encounter occurred less than a few thousand year ago. The object responsible for causing the spiral structure must then be within a few arcminutes of the star. However, the USNO-B proper motion survey reveals no candidate object. Moreover, the probability that a field star encountered HD 100546 in the past few thousand years is very low.

astro-ph↗
arXiv2005

The Effect of Spiral Structure on the Stellar Velocity Distribution in the Solar Neighborhood

Clumps in the solar neighborhood's stellar velocity distribution could be caused by spiral density waves. In the solar neighborhood, stellar velocities corresponding to orbits that are nearly closed in the frame rotating with a spiral pattern represent likely regions for stellar concentrations. Via particle integration, we show that orbits can intersect the solar neighborhood when they are excited by Lindblad resonances with a spiral pattern. We find that a two-armed spiral density wave with pattern speed placing the Sun near the 4:1 Inner Lindblad Resonance (ILR) can cause two families of nearly closed orbits in the solar neighborhood. One family corresponds to square shaped orbits aligned so their peaks lie on top of, and support, the two dominant stellar arms. The second family correspond to orbits 45 degrees out of phase with the other family. Such a spiral density pattern could account for two major clumps in the solar neighborhood's velocity distribution. The Pleiades/Hyades moving group corresponds to the first family of orbits and the Coma Berenices moving group corresponds to the second family. This model requires a spiral pattern speed of approximately 0.66 +- 0.03 times the angular rotation rate of the Sun or 18.1 +- 0.8 km/s/kpc.

astro-ph↗
arXiv2003

Quaternionic Kähler and hyperKähler manifolds with torsion and twistor spaces

The target space of a (4,0) supersymmetric two-dimensional sigma model with Wess-Zumino term has a connection with totally skew-symmetric torsion and holonomy contained in Sp(n)Sp(1) (resp. Sp(n)), QKT (resp. HKT)-spaces. We study the geometry of QKT, HKT manifold and their twistor spaces. We show that the Swann bundle of a QKT manifold admits a HKT structure with special symmetry if and only if the twistor space of the QKT manifold admits an almost hermitian structure with totally skew-symmetric Nijenhuis tensor, thus connecting two structures arising from quantum field theories and supersymmetric sigma models with Wess-Zumino term.

math.DG↗