# Tag Info

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This relationship was discovered empirically by Henrietta Leavitt by comparing the apparent magnitudes of stars in the Magellanic clouds. Since these clouds are far away (200,000 ly) and relatively small (7,000 ly), the difference in distances to the 47 different Cephid variables she observed could account for only a small difference in brightness. By ...

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Why not read his original paper? It's fairly short by today's standards, despite being such a monumental turning point in our understanding of the size and nature of the Universe. In short though, Hubble measured the distance to Cepheid's the same way anyone does. There is a distinct relation between the luminosity oscillation period of the star and the ...

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Some classical Cepheids pulsate simultaneously in two or even three modes. Their lightcurves can be explained as a overposition of fundamental plus overtone modes. The terminology you used is also found in this paper (where you have also other references): "the discovery of many double-mode Cepheids (DMCs) pulsating in both the fundamental and first-...

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Cepheid pulsations The basic description of the mechanism behind Cepheid pulsations is given here: The accepted explanation for the pulsation of Cepheids is called the Eddington valve,[38] or κ-mechanism, where the Greek letter κ (kappa) denotes gas opacity. Helium is the gas thought to be most active in the process. Doubly ionized helium (helium whose ...

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Am I naive to think that it is necessary to build up a nice, complete light curve with dense points in time in order to use the photometry for precision distance calculations? No, the more I read about it, the more difficult it seems to be. In principle, if you sample regularly and often, you should eventually get a light curve, unless the period is the ...

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Cepheid variable stars and exoplanets transiting stars have very different light curves (the relation between brightness and time). Exoplanet light curve from NASA: Cepheid variable light curve from astronomynotes.com: Also, as Rory Allsop points out, the scale of the change in brightness is very different. Cepheid variables can be seen at great distances,...

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INT refers to the floor function. So $\mathrm{INT}(x)$ is the largest integer not exceeding $x$. In this case, the function is used to get the fractional part of $\frac{\mathrm{HJD}-T_0}{P}$, i.e. the part after the decimal point. So if for example $\frac{\mathrm{HJD}-T_0}{P}=3.4$, then $\frac{\mathrm{HJD}-T_0}{P}-\mathrm{INT}\left(\frac{\mathrm{HJD}-T_0}{... 3 This graph is not the light curve of a cepheid. It is used to find the average brightness of the star, and from that, estimate its distance. The rate at which cepheids pulse is related to their average luminosity (and so their average absolute magnitude). This graph relates the period to their average absolute magnitude. To use the graph, observe a cepheid ... 3 Casertano et al. used the period-luminosity (P-L) relation of Cepheid variables as a sanity check on Gaia DR1 parallaxes. They chose Cepheid variables within the Milky Way having parallaxes in TGAS (Tycho-Gaia astrometric solution, reusing Hipparcos data for a head start). The period and apparent magnitude come from ground-based photometry (van Leeuwen et al.... 3 Finally, after searching quite a deal, I found this paper which would aptly answer the question. The paper from 1999 published by Pietrzynski and Udalski in Acta Astronomica lists the Cepheids in the star clusters of Magellanic Clouds. 2 Since it seems you don't know the equations, I will try to keep it simple. However, just keep in mind that, in principle, there is no difference between Galactic and extragalactic Cepheids, in this context. Now, we know that a Period-Luminosity relation holds for the Cepheids:$P\sim L$Where$P$is the pulsation period observed from the Cepheid, and$L$... 2 It is admirable that you are tackling this type of problem as a high school student, but I really think that some of these topics are out of your grasp currently, partly because of the highly technical nature, but also because of your lack of access to the necessary data. For one thing, you say you have V-R colors as a function of time, but all these ... 2 I'm not sure what you are actually trying to do. Radial velocity isn't generally measured, it is computed from the projected velocity. But if I take you at your word, that your raw data is radial velocity, then that simplifies things. If you know the period,$P$, and you know the$v$AND if you know the theoretical relationship between them$v = f(p)\$ then ...

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The "drift-and-shift" (DASH) mode was described in a paper by Momcheva et al. (2016), and works the way you supposed: a sequence of nearby images is taken using blind offsets without guide-star recalibration: move to the first field and take an image (possibly first acquiring a guide star), move to a nearby target field and take another image (no guide star ...

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It is correct that we can't observation stars in other galaxies with the unaided eye. But with telescopes, we can see much more, including individual stars in other galaxies. We certainly have plenty of examples including several galaxies that don't orbit the Milky Way (and some outside the Local Group!) Indeed, it was because we can detect individual ...

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Vizier is a good resource for finding catalogs. Searching for "SMC+cepheid" I found a related paper (Udalski et al. 1999) with additional data http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=J/AcA/49/437. You can also look for "Similar Catalogs" though it may or may not be useful in this case.

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[In addition to the answer already provided by Py-ser] In the body of a Cepheid, there is a regular or periodical variation of difference between the gravitational pressure and radiation pressure. This radiation pressure is due to the consumption of fuel in it, lighter elements like hydrogen and helium undergoing nuclear fusion into forming heavier elements....

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