# Tag Info

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The colour of a star is due mostly to its temperature. Except at extreme velocities, the red-shift won't affect the light enough to change the visible colour. To detect a red or blue shift you need some marker in the spectrum that can be measured accurately. The spectrum of light from a star will contain dark lines, called Fraunhofer lines, which are due ...

7

The luminosity of normal stars is a strongly increasing function of mass. e.g. $L \propto M^3$. If another star is "hidden" in a binary system, then it is of lower mass. So the amount of hidden mass is less than what is seen. Of course this can (and is) be accounted for when estimating the mass present in luminous matter because we know typical ...

6

Millimeter and sub-mm observations (110-300 GHz = 2.7-1.0 mm) are sensitive to the thermal emission and provide a brightness temperature of airless bodies like the Moon or asteroids. The radio emission is from just below the surface/skin of the body (down to $\sim10\lambda$ so ~1 cm in this case) and so is also sensitive to the thermal inertia and ...

5

In Farihi et al. (2013) (it's a Science paper, unfortunately I'm not sure its content is freely accessible), they actually measured metal excess in the white dwarf GD 61 (for an astronomer, everything that is nor hydrogen neither helium is a metal). Due to high surface gravity in white dwarfs, any heavy element should sink rapidely in its atmosphere; ...

4

The first thing to notice is that the Local Interstellar Cloud, in which the Sun is evolving right now, is a fairly diffuse region, with a typical density of about one to a few particles per cubic centimeters. Clouds with such low density are actually mostly atomic; as you can see on this plot (Snow & McCall 2006, adapted from Neufeld et al. 2005): It ...

3

I'm not a spectroscopist, but, I know a fair bit about spacecraft data reduction. CRISM is a spectrometer that's very sensitive, but it needs more light than it can get by just riding along with the spacecraft, so it slews in the reverse direction of motion (that's why CRISM images have that hourglass shape). Despite that, it STILL has some light issues ...

3

The chemical composition of stellar atmospheres is usually obtained from absorption lines. The analysis ingredients are a good spectrum, a model of the temperature and density structure of the stellar atmosphere and a catalogue of atomic and molecular transitions. It is these latter things that I think you seek. Such "linelists" are found in many places; ...

3

The equilibrium temperature of the Earth, $T_E$, scales roughly as $L^{1/4}$, which is proportional to $R^{1/2} T$, where $L$, $R$ and $T$ are the solar luminosity, radius and temperature. The actual approximate relationship is derived by equating the power received by the Earth, which is proportional to the solar luminosity $L$, with the power radiated by ...

3

A few sources come to mind to add to MAST and Sloan. Data releases from the SAMI Galaxy survey, which contain (or will eventually contain) emission line spectra for about 3500 galaxies. The papers for the first two releases can be found [here] and [here]. Another (smaller and older) dataset can be found at the Penn State Center for Astrophysics. It contains ...

2

In this case itseems to mean that the depth of the line is 7 times its error bar below the continuum level. Impossible to answer. You say it can't be done, but the authors say that they fitted a Gaussian. You either use a rough estimate (attributable to Cayrel de Strobel 1988) of $$\Delta {\rm EW} \sim 1.5\frac{\sqrt{RP}}{{\rm SNR}},$$ where $R$ is the ...

2

The answer turned out to be that I was pushing the models package too far with the data that I was giving it. More careful background subtraction and much more localised fitting helped greatly.

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Really, all cameras/detectors are greyscale detectors. Every pixel in a CCD detector puts out a single number for the number of photons it detected. To create an RGB image you need three filters. If you have 3 detectors, you can put a different filter in front of each and get 3 numbers at once. If you have 1 detector, then you take 3 measurements with a ...

1

OP here. For those who care, I think I figured out a solution; for my particular situation at least. I'm pretty sure that as long as I use reference images for each wavelength I will be able to measure the reflectivity of my samples using RGB images converted to grayscale. Much like in spectrophotometry, I will be calculating the following ratio: sample(...

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