Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [photometry]

The tag has no usage guidance.

0
votes
1answer
18 views

Normalizing the supernova spectrum by photometry

I have a SN spectrum here (already reduced) that seems to have some artifacts. Professor tells me that I may have to normalize it using photometry. As far as I understand, I just have to multiply it ...
2
votes
2answers
68 views

Why do we use filters in telescopes for astronomical imaging?

I have read that if we image without a filter we get no information about the color or SED of objects. Can anyone elaborate the reasons for using filters for imaging/photometry? What happens if we ...
2
votes
0answers
29 views

Why can't I use automatic photometry on IRIS?

I'm trying to do photometry on my stacked images of the night sky, but when I use the program IRIS and try to do automatic photometry, it always says it's a wrong image number and in every example of ...
1
vote
0answers
23 views

Regression line in a colour-colour diagram

A colour-colour diagram (CCD) like this compares the difference in magnitudes at different wavelengths. The trend in the pattern of colour-colour comparisons tells us about what type of source the ...
2
votes
1answer
59 views

How bright is Andromeda's center, in magnitudes per square arcminute or something similar?

I'd like to know how bright the Andromeda galaxy's core is as an extended object, not the total integrated brightness. Ideally a contour map or scan across the center might show brightness in ...
3
votes
2answers
57 views

Observing eclipsing binaries

In a matter of weeks, I will be performing my first observation using a 25-cm Newton telescope (+CCD camera) and would be grateful for advice regarding an otherwise basic research that I have decided ...
1
vote
3answers
67 views

How do I obtain the brightness of a star in the night sky?

I am planning to conduct a research which involves observing the brightness of a star. So far, I haven't been able to obtain much information as to how I may go forward with the observation process. I'...
1
vote
0answers
55 views

What is the canonical method to calculate the surface brightness limit of a 2D image, e.g., in a 1 arcsec2 aperture?

What is the canonical method to calculate the surface brightness limit of a 2D image, e.g., in a 1 arcsec2 aperture? ...if image has erg/s/cm2 units and each pixel has some arcsec2 dimension.
4
votes
1answer
141 views

What is equation of straight line for a ideal blackbody on the color color diagram?

The color-color diagram is a plot between $U-B$ vs $B-V$ values. For a ideal blackbody, what is the equation of this line? In other words, what does the linear relation between $U-B$ and $B-V$ look ...
0
votes
0answers
73 views

How to measure uncertainty in flux density?

Let's say I have an image of a galaxy that is 10 pixels, and the pixels have values 1, 2, ... 10 Jy/beam. If the RMS background noise is 1.5 Jy/beam, and I want source detection at 3 sigma level (...
0
votes
0answers
47 views

Where can I get radial velocity data on HDE 226868/Cygnus X-1 and A0620-00?

I want to plot the radical velocity curve of HDE 226868/Cygnus X-1 or A0620-00 from REAL data. Where could I get the full data from spectroscopy and photometry?
1
vote
1answer
42 views

How to find if a set of objects lies within a given resolution (5 arcsec) on a telescope?

I am new to astronomy and I was given the task of finding out if there are objects which can't be resolved by a telescope of resolution 5 arcseconds. I was given the values of RA and Dec of these ...
1
vote
1answer
77 views

What do “star noise” and “sky noise” refer to for TESS (Transiting Exoplanet Survey Satellite)?

The eoPortal article for TESS (Transiting Exoplanet Survey Satellite) gives a fairly in-depth summary of the space telescope design and planned operation. Some further background information on its ...
0
votes
1answer
135 views

Aperture photometry uncertainties

Suppose I have a 2D data array with number of counts in each pixel (i.e., this is the image array). Suppose I have another 1-1 mapped same-shape data array that gives the 1-sigma Gaussian standard ...
0
votes
0answers
56 views

compute magnitude in vega system from fluxes in the unit of photons per unit area

I downloaded a catalogue of fluxes in the unit of photons per unit area from here. I don't know how to convert these fluxes to magnitudes ($m$) in the vega system. I use following equations for ...
1
vote
0answers
26 views

Making photometry and astrometry with Maksutov OTA

I am developing a project of astrometry and photometry in my astronomy club. We are going to create a group interested in photometry of clusters and binary stars, but also, we want to use the images ...
1
vote
0answers
45 views

How to derive uncertainty on photometric magnitudes of extended objects?

Suppose I have an astronomical image in some bandpass and I do photometry of an extended source (i.e., a galaxy). I measure an enclosed magnitude within my aperture or galaxy profile. What is a ...
1
vote
1answer
64 views

Transit Depth Color Versus Transmission Spectroscopy

One of the tools being developed for the study of exoplanets is called transmission spectroscopy - basically looking at how passing through the exoplanet's atmosphere changes the spectrum of the star. ...
2
votes
2answers
90 views

What is the unit used for star brightness due to skyglow?

What is the name and unit of the quantity in which star brightness due to skyglow is measured? How can it be measured from RAW image files of stars?
3
votes
1answer
160 views

Why do different instrumental filters use different magnitude systems (Vega vs AB)?

Suppose I wanted to construct the spectral energy distribution (SED) of an object. Further suppose I observe this object through the 9 broad-band filters using the Subaru Suprimecam (just for an ...
2
votes
0answers
97 views

Convert RGB pixel value of an image to limiting magnitude

I have taken photos at different exposures from different places of the Orion constellation. I wish to find the effect of skyglow on the limiting magnitude of stars in the Orion constellation. How can ...
1
vote
1answer
339 views

How do I get flux density when I have mJy/beam , beam size and pixel size in an astronomical image

I have a fits file of the galaxy m87 produced by SCUBA 2 and I am wondering how I obtain the fluxes at 450 and 850 microns. the output image gives pixel magnitudes in mJy/beam where I want to find eh ...
2
votes
4answers
90 views

Is TESS replaceable by gound-based-small-telescope arrays?

TESS is designed to perform an all-sky transiting exoplanet survey. TESS's survey will focus on nearby G, K and M type stars with apparent magnitudes brighter than magnitude 12. Approximately 500,...
1
vote
3answers
92 views

Cubic spline interpolation in light curve of pulsating stars

Why is cubic spline interpolation used to analyze light curve of pulsating stars? Is there any scientific justification of such usages? One example of using the cubic spline interpolation is here, ...
7
votes
1answer
93 views

Has star KIC 8462852's 3 year long Kepler-fading continued after the primary Kepler mission ended?

BACKGROUND May 11, 2013 the Kepler space telescope ended its primary mission. Data captured until then showed that the now famous "Tabby's star" or "Boyajian's star" (KIC 8462852) had been fading ...
6
votes
1answer
1k views

What is the ugriz magnitude system?

While studying photometric redshifts, I came across the ugriz (or u'g'r'i'z) system for classifying magnitudes of galaxies, but I didn't find much information on the internet about how it works. Can ...
1
vote
0answers
40 views

Interstellar reddening for Cepheids

How were interstellar reddening values for cepheid first calculated? I mean, other than using the derived equation to get extinction-corrected magnitude of Cepheids, I want to know how to drive them ...
1
vote
1answer
53 views

What does less than one count from an x-ray detector mean? (Swift BAT detector)

I'm reading a paper about a recent x-ray burst from a suspected magnetar (A. Dai et al 2016) where they show a light curve of a burst that lasted about 10ms. (Their figure 1). The value of count rate ...
0
votes
1answer
44 views

How do I get the change in angular diameter value?

Given that I got the equation relating the angular diameter(θ) and $V$–$K$ band value, which is known as $\logθ_0=(0.262±0.004)(V−K)_0+(0.547±0.006)$ from this paper, how do I get the 'change' in ...
2
votes
0answers
44 views

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 ...
1
vote
1answer
95 views

What telescopes have observed anomalies in the light curve of Tabby's star, KIC 8462852?

KIC 8462852, the F-star that inexplicably dims by up to 20% for short periods, is still getting alot of attention. A slow continuous dimming by about 0.3% a year has been identified recently. But all ...
1
vote
3answers
559 views

Data reduction and photometry without IRAF?

The IRAF package is old. I've been looking around for a more modern software to replace it in the processes of CCD data reduction and photometry, but haven't been able to find any. The closest I've ...
3
votes
1answer
2k views

How can I convolve a template spectrum with a photometric filter response spectrum?

Suppose I have a template stellar population spectrum (say, from Bruzual & Charlot 2003) which runs from like 1000 Angstroms to 160,000 Angstroms and which has x-axis wavelength units of Angstroms ...
1
vote
1answer
27 views

How do I reduce planetary photometry to standard viewing geometry using phase angle?

I'm trying to make light curves for Pluto using old data. Most papers give magnitudes "reduced to standard viewing geometry" of r = 39.5 AU, Δ = 38.5 AU, and α = 1 degree, where r is ...
1
vote
1answer
93 views

What kinds of stars would it be possible to observe in M31 with a small amateur telescope?

I was wondering what kinds of stars would be visible in M31 and other nearby galaxies using a moderate (~8") telescope and a CCD camera. This would be a limiting magnitude of around 17. I have heard ...
0
votes
2answers
152 views

How to calculate the pixel size and beam size of an image?

I have an image with some sources in it. I need to get the pixel size and beam size of that image. How can I calculate it?
4
votes
1answer
131 views

Estimating galactic dust extinction for medium band filters

I have a set of medium-band filters and I would like to compute $A_{\lambda}/E(B-V)$ for each filter which are not reported in the literatures. The magnitudes of the objects in the photometry ...
0
votes
1answer
90 views

How to create synthetic test images of stars?

Is there any python/IDL code available to create synthetic test images of stars with and without background noise?
5
votes
3answers
475 views

Could mirrors be replaced with CCDs?

Why do telescopes use mirrors that simply reflect photons, when they instead could be covered with large sensors to register them? Reflection is all good and well, all thanks to silver and beryllium ...
3
votes
0answers
58 views

How does one find the extinction coefficient of a particular galaxy? [closed]

I am doing photometry on a number of objects in a number of different galaxies. I need the extinction coefficients for these galaxies for various filters passes. Is there some database that displays ...
3
votes
1answer
109 views

Gaia: What is the difference between CCDs used for astrometry, photometry, and spectroscopy?

My knowledge of CCDs is that these are sensors which collect photoelectrons. That's about it. What is a difference between CCDs used for astrometry, spectroscopy, and photometry? As an example, each ...
2
votes
1answer
472 views

Photometer vs. CCD-camera

The Wikipedia article on photometry says that These have largely been replaced with CCD cameras that can simultaneously image multiple objects, although photoelectric photometers are still used in ...