Skip to main content
7 votes
Accepted

Are there really confined Globular Clusters?

You are asking for a star cluster that sits at the bottom of an infinite potential well. Such clusters do not exist because they are largely the source of the potential that they reside in. There are ...
ProfRob's user avatar
  • 153k
6 votes
Accepted

highspeed black holes or neutron stars on (almost) head-on collision course and kinetic energy

I think it's a fun question, and I can answer some of it. If their event horizons don't "touch" I'd assume their courses will change considerably but it would be a normal flyby - right? While ...
userLTK's user avatar
  • 24.1k
6 votes

List of Moving stars on the northern hemisphere? [Stellar kinematics]

What you're looking for is stars with "High Proper Motion". A Google search of "High proper motion stars" will provide a number of such lists. A quick look at Wikipedia gives this link: https://en....
John Hunt's user avatar
4 votes
Accepted

In 31.5kyr, Epsilon Eridani and Luyten 726-8 will be < 1ly close; but how distant from the Solar system?

These stars are currently moving away from us, in the case of Epsilon Eridani, at 15.5 km/s. In 31500 years they will be further away than they are now, the distance can be calculated by applying ...
James K's user avatar
  • 123k
4 votes

List of Moving stars on the northern hemisphere? [Stellar kinematics]

SIMBAD allows you to search for stars given various criteria. I searched for: Dec > -20 (easily visible from most locations in the Northern hemisphere) Vmag < 4 (easy naked eye objects) pm > ...
James K's user avatar
  • 123k
4 votes
Accepted

What are typical peculiar velocities?

From the virial theorem, peculiar velocities resulting from gravitational processes generally have magnitudes of the order of $$ V \sim \left(\frac{GM}{R}\right)^{1/2}, $$ where $G$ is the ...
pela's user avatar
  • 38.6k
3 votes

Are there really confined Globular Clusters?

Disregarding the example of globular clusters (which are all undergoing evaporation, as ProfRob points out), there are a couple other candidates for "isolated" astrophysical systems. The ...
Tom Donlon's user avatar
3 votes
Accepted

Derive LOSVD from galaxy spectrum, using fourier method

There were a few mistakes in the treatment of my spectra before fourier transform in the first place. So missing steps were: 1.) The spectra should be averaged to 0 by subtracting the median. 2.) You ...
trynerror's user avatar
  • 849
2 votes
Accepted

Extracting kinematics from stellar spectra. Why are template stellar spectra necessary?

(Optically thin) Emission lines in nebulae are generally unresolved and have simple shapes that might be approximated by Gaussians. Stellar spectra are complicated - there are blends, there is ...
ProfRob's user avatar
  • 153k
2 votes

Does the Abell 1689 supercluster have angular momentum?

I have not studied this galaxy cluster specifically. However, I can speak about systems like galaxy clusters that have a large number of bodies that are in close enough proximity to have a non-...
Unique Worldline's user avatar
2 votes

highspeed black holes or neutron stars on (almost) head-on collision course and kinetic energy

If the two black holes miss are more than a few Schwarzschild radii apart at closest approach then what will happen will look very much like the pure Newtonian solution -- similar to a close encounter ...
Steve Linton's user avatar
  • 10.3k
2 votes

How does instrumental dispersion work?

$x$ is in terms of $\log \lambda$ because increments in $\log \lambda$ correspond to increments in line of sight velocity. e.g. see Why do linear velocity redshifts correspond to linear pixel shifts ...
ProfRob's user avatar
  • 153k
1 vote

Are there really confined Globular Clusters?

Well, things like small asteroids are self-gravitating and confined to a pretty well defined volume. We believe they are approximately in thermal equilibrium. But it isn't gravity that brings them to ...
John Doty's user avatar
  • 1,909
1 vote
Accepted

What am I doing wrong in this ppxf application?

The velscale keyword defines the spacing of the spectrum's wavelength vector, in velocity (km/s) units. Look in the ppxf code (in ppxf.ppxf_util) for the log_rebin ...
Peter Erwin's user avatar
  • 17.1k

Only top scored, non community-wiki answers of a minimum length are eligible