31 votes
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How hard is it to find the Sun's "sisters?"

Here are the problems/issues: Most stars are born in clusters/associations but a cursory investigation of cluster demographics with age reveals that the vast majority of clusters do not survive to old ...
ProfRob's user avatar
  • 149k
17 votes
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Whereabouts of the Pleiades

With the exception of the Andromeda galaxy and the Magellanic clouds1, every star, star cluster and nebula that is visible to the naked eye is part of the Milky Way. The Pleiades is a star cluster in ...
James K's user avatar
  • 119k
13 votes

Whereabouts of the Pleiades

To give you a perspective the Milky Way Galaxy is between 150,000 and 200,000 light years in across. The Pleiades is less than 450 light years from Earth. In a galactic perspective the Pleiades is ...
Bob516's user avatar
  • 1,467
12 votes
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Why do stars born in a cluster finally disperse?

The boundedness or otherwise of clusters remains to be established in most cases. The vast majority of clusters become unbound and disperse at a much younger age than the Pleiades. Or they may be born ...
ProfRob's user avatar
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10 votes
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What cluster of stars is this with a "dark donut" to one side?

OK, having (finally) actually looked at the video, it's clear that Szymanek is looking at the center of M33. There is in fact a nuclear star cluster in the center of that galaxy; not knowing the field ...
Peter Erwin's user avatar
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7 votes
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Is every star formed in an open star cluster?

The question is still an open matter of current research. It seems to be true that the vast majority of star formation takes place in groups and aggregates of various sizes - from a few stars to ...
ProfRob's user avatar
  • 149k
7 votes

Whereabouts of the Pleiades

This screen grab from the program Where is M13? shows the location of the Sun and Pleiades in our galaxy. The Sun is the orange dot, the Pleiades the yellow dot.
MichaelB76's user avatar
6 votes
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Jacobi vs tidal radius for star cluster

In the book Galactic Dynamics by Binney and Tremaine (second edition) there is a whole section explaining the difference between the Jacobi radius and the tidal radius (page 677-chapter 8). Here, $...
charles's user avatar
  • 86
6 votes
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Bica 5 open cluster

Yes, this is the fifth cluster in the catalogue by produced by Eduardo Bica et al. You can see its listing in a list of clusters. That notes it is also known as MWSC 1964 and you can find it in Simbad....
James K's user avatar
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5 votes
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Difference in HR diagram clusters

The main difference is due to the age of the cluster. In our Galaxy the globular clusters are old ($>10^{10}$ years) and as a result the main sequence turn-off is down at something like $0.9 M_{\...
ProfRob's user avatar
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5 votes
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Calculating obital velocity from radial velocity

You can't without assuming something about the overall velocity. The radial velocity is one component of a velocity vector; you are missing the other two components, which could in principle be ...
ProfRob's user avatar
  • 149k
4 votes

Pleiades galactic coordinates

The galactic coordinate system is centred on the Earth (not the galactic centre) with 0 degrees longitude in the direction of the galactic centre. (as measured by observation of the distribution of ...
James K's user avatar
  • 119k
4 votes
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What are the smallest star clusters affected by Galaxy Rotation Curve?

Yes, dwarf galaxy rotation curves are affected -- in fact, they tend to require relatively more dark matter than is required to explain the rotation curves of giant galaxies like the Milky Way. The ...
Peter Erwin's user avatar
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4 votes

If a cluster of stars in dynamical equilibrium falls into a much larger blob of dark matter, will it get hotter and expand? Will it stop?

Yes, what you are proposing is essentially the accretion of dwarf galaxies/globular clusters onto larger bound objects. As the gravitationally bound cluster falls towards the more massive object, it ...
Tom Donlon's user avatar
3 votes
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integration of velocity distribution f(v)

You need to divide 60,000 by the integral of this function from zero to infinity. That will then give you the fraction of stars with a velocity (I think it is probably speed, not velocity?) between 0 ...
ProfRob's user avatar
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3 votes
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Which A. M. Fridman is the author of this paper on gravitational stability?

It's Alexey Maksimovich Fridman. I think that's pretty clear from the respective research interests of the two scientists, but we can go deeper... Let's start off with the author of your 1971 paper. A ...
Peter Erwin's user avatar
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3 votes

How hard is it to find the Sun's "sisters?"

Stand on dune in a desert. Take a handfull of sand, all crushed from the same rock. Now close your eyes, Hold your hand up to the wind, let the wind blow all but one of the grains of sand, somewhere. ...
PcMan's user avatar
  • 279
3 votes
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Understanding Scatter in Data collected for HR Plot

So, scatter in observational measurements of clusters in the HR diagram is mainly, in my experience, caused by 3 things: observational errors, binaries and contamination. As you mentioned, there are ...
ohrkzt's user avatar
  • 161
3 votes

Pleiades galactic coordinates

You can use a coordinate converter, such as the one found here to change from RA, Dec to $l, b$. The coordinates of an object do not directly tell you whether something is a thick/thin disk object, ...
ProfRob's user avatar
  • 149k
2 votes

Natural units of star clusters angular momentum and energy

Using unit analysis, I've found that a natural unit of angular momentum should be \begin{equation}\tag{1} L_0 = \frac{G M_{\odot}}{c} \approx 8.816 \times 10^{41} \, \text{kg} \, \text{m}^2/\text{s}. \...
Cham's user avatar
  • 273
2 votes

Dataset containing list of known globular clusters

So far we have about 150ish known globular clusters in the milky way. A list of all the known ones can be found HERE. This includes their locations (may be slightly shifted by now as they were correct ...
MCG's user avatar
  • 795
2 votes

Jacobi vs tidal radius for star cluster

In the paper "A million binaries from Gaia eDR3: sample selection and validation of Gaia parallax uncertainties" El-Badry et al (2021) the Jacobi radius, in the context of orbiting binary ...
George's user avatar
  • 21
2 votes

Difference in HR diagram clusters

So, @ProfRob's answer is absolutely amazing and covers the bulk of star-cluster properties that I could think of. Nevertheless, since the question specifically asked for HR diagrams of open vs. ...
guilimberg's user avatar
2 votes
Accepted

Fitting isochrone on color magnitude diagram obtained from growth india telescope for M67

To put an isochrone on your colour-magnitude diagram, then you need those isochrones to be predictions in terms of colour and magnitude. There are models out there which do predict isochrones in terms ...
ProfRob's user avatar
  • 149k
2 votes

Is there a relationship between stars' absolute magnitude, spectral class and relative location in a cluster?

Stars born together in clusters have more-or-less the same age. As a rule of thumb, any spread in age, measured in millions of years, is smaller than the extent of the cluster in parsecs. For most ...
ProfRob's user avatar
  • 149k
2 votes
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how to calculate the half-mass radius and tidal radius of a (simulated) globular cluster

Your first question is about computing, not astronomy. You find a cumulative histogram of distance from the centre of mass and where that reaches 50% of the stars. As to your second point, there is no ...
ProfRob's user avatar
  • 149k
2 votes
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Unusual amount of white dwarfs in star clusters in my analysis

You don't have a horizontal branch, which would have an absolute magnitude of $\sim 2$ and you don't have a massive population of white dwarfs, which have a sequence that parallels the main sequence ...
ProfRob's user avatar
  • 149k
1 vote
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Mass estimate for cluster NGC2516?

NGC 2516 is somewhat richer and more massive than the Pleiades. A careful look at the mass function suggests there is about $1000 M_{\odot}$ in stars $\geq 0.3 M_{\odot}$, within the central 0.9 ...
ProfRob's user avatar
  • 149k
1 vote
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Help me identify a cluster

Since this appears to be a screenshot of Eyes on Exoplanets, I searched for "exoplanet 485" and found Kepler-485 b. With the colors exaggerated, the label area could be "Kepler-485" in yellow ...
Mike G's user avatar
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