Questions tagged [radial-velocity]
The radial-velocity tag has no usage guidance.
45
questions
35
votes
3
answers
2k
views
If Alpha Centauri A's solar system exactly mirrored our own, what would we be able to detect?
Suppose there was an exact replica of our solar system 4.4 ly away (people included). What would we be able to detect and with what telescope(s)? Which planets? Could we detect radio transmissions and/...
- 451
11
votes
4
answers
9k
views
Is Earth's Surface "In orbit"?
I'm having trouble understanding relative angular/tangential speeds at increasing altitudes above Earth's surface. In particular, I find this comparison of tangential velocities on Wikipedia very ...
- 221
10
votes
1
answer
745
views
What are the challenges in finding Earth-like planets via the radial velocity method?
[I have re-asked this, because it was a good question by @Banyan, which was deleted whilst I was composing an answer.]
Most exoplanets that are found by the radial velocity ("Doppler wobble")...
- 146k
7
votes
2
answers
478
views
Does the expansion and contraction of a variable star affect the measured radial velocity?
I've measured the heliocentric radial velocity of Beta Cephei using the doppler shift of the helium lines, I corrected for earth's motion using the doppler shift of the oxygen in the atmosphere. I ...
- 235
7
votes
1
answer
443
views
Using masers to measure rotational velocity of a galaxy
When measuring the rotation velocity of a galaxy, most of the times we can only directly measure radial velocity, by looking at the redshift.
I read in a lecture slide that some times it is possible ...
- 4,371
5
votes
2
answers
204
views
Radial Velocity Clarification Sought
According to Google, radial velocity is "the velocity of a star or other body along the line of sight of an observer".
The radial velocity of Sirius according to Google is −5.50 km/s.
If the ...
- 1,301
5
votes
1
answer
134
views
How are exoplanets with 10,000 day periods discovered with the radial velocity method?
The radial velocity technique has apparently been used to discover exoplanets with extremely long orbital periods of ~10,000 days. For example, see this link:
https://exoplanetarchive.ipac.caltech....
- 357
4
votes
1
answer
282
views
Determining period of an exoplanet using radial velocity data
I've spent an incredibly large amount of time trying to wrap my head around how the period is computed using just solely the raw data for the radial velocity. I've tried my hand with some nonlinear ...
- 101
4
votes
1
answer
278
views
Why is there an extra peak in the Lomb-Scargle periodogram?
I was messing around with some radial velocity data from NASA's Exoplanet Archive and the Lomb-Scargle periodogram for Pegasi 51 yielded two very sharp peaks. One corresponds to about 4.23 days which ...
- 101
4
votes
1
answer
140
views
How to phase fold data when periodicity change is known as d$\omega$/d$t$?
How can I obtain a phase-folded phase - velocity diagramme from a time series of radial velocity data when it is known that the periodicity changes as $\frac{{d}\omega}{{d}t}$?
Without $\frac{{d}\...
- 115
4
votes
0
answers
176
views
How to determine the time of periastron passage (T) of a single lined spectroscopic binary?
I am working on finding spectroscopic elements of a single lined spectroscopic binary. All I have is irregularly spaced radial velocity data which needs to be phase folded to plot a velocity curve (RV ...
- 53
4
votes
0
answers
48
views
Cross-correlations between Lagrange and Fourier synthesis
In the context of forecast for large surveys, I have to make cross-correlations between 2D (with angular coordinates of Lagrange transformation for GC photometric and Weak Lensing) and 3D (Fourier ...
user16492
4
votes
0
answers
82
views
Radial velocity exoplanet search - can mathematical details be explained? (Bayesian periodogram MCMC)
Radial velocity (RV) is one of main methods for exoplanet search.
The popular description of the method sounds simple - one should measure periodic Doppler variation of a spectral line of a star and ...
- 647
3
votes
3
answers
407
views
Why is it impossible to estimate the inclination of an exoplanet with the Radial Velocity Method?
The formula of the radial velocity is:
$$v_i= V - K(\sin(f_i+\omega)\ + e\sin\omega),$$ with
$$K = \frac{m_p}{m_s+m_p}\frac{na\sin i}{\sqrt{1-e^2}}.$$
Being $V$the systematic velocity of the system,
...
- 1,800
3
votes
1
answer
82
views
How to determine the amplitude of RV curve for eccentric orbit?
How to determine the amplitude of RV curve $$K_1$$ for eccentric orbit when the anomaly is not known, please? Thank you very much
Edit:
I thought that |RV_min-RV_max|/2 holds for circular orbits $e = ...
- 711
3
votes
1
answer
195
views
Radial velocity
Is there a way to calculate the radial velocity without wavelength? I can only find two formulas so far. One of them needs wavelengths and the other one needs the velocity of the star, but I have none ...
- 71
3
votes
1
answer
300
views
How spectrographs that measure radial velocities manage to translate variations in the stars' spectrum lines into the "speed" of the star?
Like ESPRESSO or CARMENES, for example. I just don't understand the process or the way these spectrographs manage to obtain the velocity of the "wobble" of the star (due to the presence of another ...
- 1,800
3
votes
1
answer
2k
views
Calculate the orbital phase when plotting the Radial Velocity data of a transitting exoplanet
I'm not quite sure how I find the orbital phase ($\phi$) of a transitting exoplanet. For example, I have this RV data in this article:
First of all, I don't know how that phase or "cycles" is ...
- 1,800
3
votes
1
answer
57
views
Radial velocities - wings and core
Why are radial velocities measured at the core and at wings of a line profile? I mean interactive measurement -- comparing the direct and flipped images of the line profiles.
What is the difference of ...
- 153
3
votes
1
answer
112
views
Radial velocity stability to spectrum shift calculation
I am engineer new to Astronomy and am trying to understand spec of an spectrograph (RV stability = 2m/s). There is a note in document saying "RV shift of 2 m/s is equivalent to a shift of the ...
- 33
3
votes
1
answer
156
views
Pair together light curve and radial velocity data of specified star
I would like to create a web application that works with light curves and radial velocities of stars with exoplanets. I found a NASA bulk data download with both light curves and radial velocities (it'...
- 313
3
votes
1
answer
352
views
Is it possible that some of the confirmed exoplanets are in fact primordial black holes?
Recently astronomers discovered a black hole lying just 1000 light-years from Earth, in a triple star system (HR 6819) that can be seen with the naked eye. This discovery has increased the possibility ...
- 593
2
votes
2
answers
906
views
How does one calculate inclination from a graph of radial velocity?
If a binary star system has a non-zero inclination, how would that show up in a graph of radial velocity?
How could I then extract the inclination from the graph?
- 427
2
votes
1
answer
192
views
Radial Velocity Graph and Rossiter Mclaughlin Effect
I am trying to understand the effect of the Rossiter–McLaughlin effect on radial velocity plots. Can someone help me and explain what exactly is happening in the red circle?
- 55
2
votes
1
answer
201
views
Star brightness data to study exoplanets with the transit method?
Can someone tell me how I can find the star brightness data to study exoplanet using transit method? The file should be in comma separated value (CSV) format or any other formats that can be latter ...
2
votes
1
answer
106
views
Radial velocity of host stars and exoplanets
I am new to astronomy/astrophysics.
(1) In the CATALOG OF NEARBY EXOPLANETS, I came across the following terms.
Please see Table 2 of the above paper. 12th column lists $v \sin(i)$ - It is the radial ...
- 169
2
votes
1
answer
136
views
Radial velocity curves
When I measure RV in a program for more spectral lines, will it be equivalent? I mean I measure RVs of a line in blue spectral region, RVs of a line in red spectral region... Many thanks.
- 155
2
votes
1
answer
63
views
Average velocity of stars in globular cluster
This article explains how to calculate the mass of a globular cluster. The first equation is
\begin{equation}
v^{2}_{1D} = \sigma^{2}_{r}
\end{equation}
Can someone please elaborate why this is the ...
- 217
2
votes
1
answer
60
views
Estimating the radius of a non-transiting exoplanet
I need to know the timescale of tidal locking of a non-transiting exoplanet. For that, I need to know (or at least have some constraint of) its radius (Gladman et al. 1996):
$$T_{lock} = k \frac{a^6}{...
- 1,800
2
votes
1
answer
119
views
Why does the velocity dispersion within a galaxy cluster decrease as a function of radius?
In the paper 10.1093/mnras/sty2379, there are plots showing the velocity dispersion as a function of radius.
Focusing on the right-hand plot, non-merging normal clusters, intuitively why should the ...
- 53
2
votes
1
answer
151
views
When graphing radial velocity measurements, whats the relationship between days and the orbital phase
I graphed the radial velocity measurements for various planets, however, I am able to calculate the RV and the phase but whats the translation between phase and days. I want it to be days vs RV.
- 83
2
votes
1
answer
1k
views
Looking for a routine to correct for Local Standard of Rest (LSR)
I've been scanning the Milky Way with a Small Single Dish Radio Telescope, obtaining Spectral data with a Span of ~ 2 MHz, centered at the 21 cm line. With this information I can derive a relative ...
- 605
2
votes
1
answer
293
views
Computing radial-velocities from Cross Correlation data
How can I better fit a Gaussian curve to a CCF so that I get the most precise RV value? The image below shows the fitting where I compared the fitting by weighting by the uncertainties and not. There ...
2
votes
0
answers
39
views
Provided a relative flux v/s wavelength plot, how can I calculate the radial velocity of an exoplanet? [closed]
I imagine the relativistic version of the Doppler effect would be appropriate but I'm not entirely sure since flux is a measure of intensity. Alternatively, where could I find redshift data for ...
- 101
2
votes
0
answers
264
views
Using the 'exoplanet' module to fit a radial velocity curve for a binary star system
As part of a project, I am trying to fit a radial velocity curve using the tutorial for the binary star system (EBLM J0608-59) My code is quite similar to the tutorial, but as it is only one body ...
- 21
1
vote
1
answer
125
views
Why histogram does not look like the Gaussian curve?
I have data consisting of radial velocities and times (covering about 10 000 days). The radial velocity changes with a period. I tried to find out the period using Stellingwerf's method (it was ...
- 495
1
vote
1
answer
837
views
Wavelength and radial velocity
What is the relation between the wavelength and the radial velocity? I have a data: wavelength and intensity and I would like to plot intensity with respect to radial velocity - similarly as in the ...
- 155
1
vote
1
answer
309
views
derivation of binary mass function for eccentric orbit
When investigating methods to detect exoplanets, I learned about binary mass function(BMF) which could be applied to obtain radial velocity and the mass. I've derived BMF for a circular orbit, but I ...
- 21
1
vote
1
answer
474
views
What does correcting for LSR mean in galactic velocities?
This is a two-part question, but both parts are related:
I'm aware that modern astronomical software can correct velocities for the local standard of rest (LSR), but what does that really mean? As in,...
- 11
1
vote
0
answers
37
views
Time average of radial velocities of multiple galaxies
Equation (34) in this paper shows an average radial velocity. The author wrote that the value was obtained by measuring the radial velocities of many galaxies in the cluster of galaxy and by averaging ...
- 217
1
vote
0
answers
47
views
How to calculate radial velocity from redshift? [duplicate]
Ok, I know the question sounds silly, but please hear me out (at the very end it will probably still be silly though, albeit maybe differently).
I'm trying to create a visualization of the galactic ...
1
vote
0
answers
182
views
Plotting GAIA barycentric radial velocity data with python
Does anybody know of a good tutorial on how to use python and astropy to generate plots of GAIA, RAVE or any other database of barycentric (heliocentric) radial velocity data of stars in our galaxy?
...
0
votes
1
answer
129
views
Determining masses from radial velocity curves of eclipsing binaries
Is the statement
From radial velocities or astrometry for eclipsing binaries, one obtains masses.
wrong, because only minimal masses can be obtained?
- 495
0
votes
1
answer
461
views
Doppler Spectroscopy - Finding mass of an exoplanet
An astronomer, T observed the spectrum of a distant star X. The spectral lines were observed to have tiny blueshifts and redshifts regularly with a period of 1.27 years. T concluded that the star is ...
- 109
0
votes
0
answers
21
views
What percentage of Earth-sized planets in a habitable zone can be detected by the radial velocity method?
What percentage of Earth-sized planets in a habitable zone can be detected by the radial velocity method?
I understand that larger planets and closer planets are detected more easily; and I assume ...
- 143