Unanswered Questions
100 questions with no upvoted or accepted answers
6
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What are the pros and cons of different types of echelle spectrograph cross-dispersers?
Echelle spectrographs, operating at high resolving power, typically consist of an echelle grating with a low numbers of lines/mm, used with high diffraction orders (often $n=$50-100). To separate the ...
- 30.7k
6
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119
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Need help understanding stellar spectroscopy data from ESO
The European Southern Observatory webpage has a web page that has tabular spectrogram data from A. J. Pickles, University of Hawaii. There are over 130 .dat files there. Each one represents a ...
- 161
5
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457
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Why does titanium oxide around Betelgeuse produce this particular sawtooth-shaped absorption spectrum?
Betelgeuse Just Isn’t That Cool: Effective Temperature Alone Cannot Explain the Recent Dimming of Betelgeuse suggests that the recent dimming might be caused by increased optical absorption by dust ...
- 30.7k
4
votes
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425
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Calculation of average FWHM by PSF fitting of all the detected stars in the fits image
I need to calculate the FWHM of all the stars detected via the DaoStarFinder package/any other package by performing PSF fitting in Python. Here is the code for my detection.
...
- 111
4
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42
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Fitting a line or polynomial to optical and radio SEDs
I've been trying to fit functions to plots showing photometric data for AGN from both optical and radio measurements, such as:
but my supervisor says that this shouldn't be done; the radio and ...
- 126k
4
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0
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52
views
How does SDSS estimate photometric redshift of sources?
I'm looking through the data in SDSS DR 12:
...
- 2,620
4
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0
answers
54
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What happens to the non-fusion formed metals in stars?
Let’s consider a population I star of some given metallicity.
I know that depending on the type of star, different structures are possible with convection zones and radiative zones trading around ...
- 3,404
4
votes
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71
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K-correction vs resizing photometric bands
Is there a difference between a K-correction (see Wiki https://en.wikipedia.org/wiki/K_correction) and simply "resizing" the bands, e.g. the 2-10 keV x-ray band, with the redshift? I've read ...
- 30.7k
4
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588
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A simple echelle spectrograph for viewing solar spectrum
On the Astrosurf website here, someone has designed a deceptively simple echelle spectrograph for viewing solar spectrum. Briefly, light from an optical fiber falls on an echelle grating and which is ...
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4
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0
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57
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How is the roll of the Hubble telescope around its axis and the dispersive direction(s) of it's spectrometer(s) managed?
Reading Dupree et al. 2020 Spatially Resolved Ultraviolet Spectroscopy of the Great Dimming of Betelgeuse (also in arXiv and summarized in Phys.org's Hubble finds that Betelgeuse's mysterious dimming ...
- 30.7k
4
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69
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How significant is the effect of galactic rotation on line broadening of carbon monoxide?
In class the other day, we were discussing observations of rotational transitions of carbon monoxide, namely, the $J=1\to0$ and $J=2\to1$ lines. We originally had assumed that both lines would have ...
- 37.3k
4
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210
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How to calculate magnitudes in photometry?
I have a passband filter $b$ and a spectrum (SED) $f_{\lambda}(\lambda)$. Often the formula I find to get the flux in that filter $F_b$ is
$$F_{b}=\dfrac{\int f_{\lambda}(\lambda) T_{b}(\lambda)d\...
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3
votes
0
answers
41
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Why MIT's Benjamin Rackham says "nearby ultracool dwarf SPECULOOS-3" would look "purplish-red, spotted, and flaring" from an airless orbiting planet?
May 15, 2024 MIT News article Newly discovered Earth-sized planet may lack an atmosphere includes the following:
“We can say from our spectra and other observations that the star has a temperature of ...
- 30.7k
3
votes
0
answers
52
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How do you calculate the reddening corrections for photometry?
I have photometric data from Gaia for a star and am trying to de-redden the colors. I need to find the reddening corrections for the photometry. I have photometry for G, BP, and RP.
To start I am ...
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3
votes
0
answers
104
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SExtractor parameters for identifying Star Forming regions
I am using SExtractor (Source Extractor) to identify Star-Forming regions in a galaxy. The problem is I am unable to choose the parameters required for it. SExtractor is just a tool to identify the ...
- 327
3
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78
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What instruments do amateur astronomers use in their ground based telescopes in order to avoid atmospheric absorption/telluric contamination?
What instruments do amateur astronomers use in their ground based telescopes in order to avoid atmospheric absorption/telluric contamination? For example, when an astronomer observes a celestial body ...
- 1,624
3
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answers
73
views
How to obtain exoplanets transmission spectra from JWST's NIRISS data of WASP96?
I was having a look at JWST's NIRISS data of WASP96 (specifically at the x1dints fits file which should be already calibrated). From this, I would like to obtain a result in a fashion similar to the ...
- 30.7k
3
votes
0
answers
80
views
S/N binning of 2D spectral galactic data
I have the 2D spectrum of the ellipical galaxy NGC 4697 taken by a long slit spectrograph. The x-direction (horizontal) corresponds to wavelength and the y-direction (vertical) corresponds to distance ...
- 849
3
votes
0
answers
636
views
DIY Sky Quality Meter: Conversion between Illuminance and Luminance
I am trying to create a homemade Sky Quality Meter (SQM) using a TSL2591 light sensor. This sensor measures Illumination (lux), but SQMs measure Luminance (mpsas). I have seen that there are many ...
- 8,452
3
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191
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Is there a tool to convert N-body RAMSES simulation file formats to GADGET 2 format in Python?
I am looking for a way to convert RAMSES files to GADGET-2 binary files because I want to use the package SimSpin (https://github.com/kateharborne/SimSpin/blob/master/R/make_simspin_file.R) which is ...
- 30.7k
3
votes
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answers
44
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Estimate the shape of an object based on flux curve
Is there an aproximation to know the shape of a dust cloud,etc based on the magnitude/flux curves of stars they transit? Example, can I know if the shape is (at least in 2 dimensions) elliptical, ...
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3
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answers
58
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Kaggle dataset for Photo-Z estimation?
I would like to use the dataset for this kaggle but the competition was private, is closed and I have been unable to contact anyone directly.
The challenge is machine learning for photo-z estimation ...
- 5,636
3
votes
0
answers
95
views
How to take into account the filter response in thermal and reflected flux density calculations?
I'm using python to calculate the thermal and reflected flux densities of a faceted asteroid model, where both equations have the Planck function present in them.
Currently, I'm integrating the Planck ...
- 41
3
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answers
95
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How were "microshutters" or other multiplexed or multi-object techniques first used in Astronomical spectroscopy?
This answer to How will microshutter arrays be used in the James Webb and future space telescopes? explains how multiple objects can be selected so that the throughput of a spectrometer can be ...
- 30.7k
3
votes
0
answers
590
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What is the difference between spectroscopy, spectrography and spectrometry?
Spectroscopy is the study of spectra, spectrography is the writing of the spectra, and spectrometry is the measure of spectra. So from an etymological perspective, there is no real difference between ...
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3
votes
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468
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How does the ESPRESSO Echelle spectrograph fold the spectrum so nicely?
The CBC News Technology and Science Q&A This ESPRESSO machine doesn't make coffee but scans the skies for habitable planets includes a nice description of ESPRESSO (Echelle SPectrograph for Rocky ...
- 30.7k
3
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answers
76
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Using the surface-brightness relation for Cepheids
I'm a high school student who is doing research about Cepheid variables.
I'm in the process of deriving distance to Cepheid using the Baade-Wesselink method, which utilises the surface brightness ...
- 8,135
3
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2k
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What is meant by ionization states?
I am going through the theory of Saha equation but I am not able to understand the concept of ionisation state? What are ionization states actually?
- 18.7k
3
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713
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How to use spectral profiles to determine luminosity class?
I know the luminosity classes are: Ia-0 ( Hypergiants ), Ia ( bright supergiants ), ... , VII ( white dwarf ).
I also have learned that you can use the presence of absorption lines ( ie. use spectral ...
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3
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71
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H-alpha velocity fields of spirals falling into a cluster
What kind of impact would you expect ram pressure stripping / tidal interactions / harassment / interactions with the cluster potential (etc!) to have on the h-alpha velocity fields of infalling ...
- 17.6k