Question
Asked 16th Nov, 2021

Are there redshift and luminosity distances for Cepheid Variable stars and RR Lyrae stars?

Do such measurements make sense? Do they exist?
Comparing redshift and luminosity distances, if that is a sensible question, may bear on the 4/3 scaling hypothesis as it relates to dark energy.

All Answers (3)

18th Nov, 2021
Davide Vatteroni
Dear Robert,
every measurement makes sense, only their interpretation(s) in the model(s) is up to debate.
The only problem that could occur in my mind is that Cepheids are too "near" us and the redshift measurement is not precise and/or under the resolution of actual made spectrograph, but if the star is far enough and you could make the two measurements (variability period and redshift) the comparison is useful to the famous "ladder problem" in astrophysics (and to make sure you calculate the distance right)
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22nd Nov, 2021
Forrest Noble
Pantheory Research Org.
Our galactic stars do not relate to redshifts but luminosity distance does apply.
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25th Dec, 2021
Suvrat Rao
University of Hamburg
Cepheid and RR Lyrae variables are well known standard candles, and important tools in the cosmological distance ladder. For example, Cepheid variables, which were discovered by Henrietta Swan Leavitt, have the property that their luminosity can be directly inferred by observing their pulsation period, which then allows one to calculate their luminosity distance, given that the observing instrument (telescope) also measures their flux.
However, although nothing stops you from making redshift measurements of relatively nearby objects, this will induce an error in any cosmological parameters inferred from these measurements (such as the luminosity distance), because the peculiar velocities of these objects would be comparable to their Hubble flow, giving you highly inconsistent results. Luminosity distances calculated by interpreting the measured redshifts as cosmological redshifts, become more reliable at large distances, where the Hubble flow dominates over the peculiar velocities.
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Gezegenleri bulmak için yıldız ışığından sakınmanın bir yolu var mıdır?
Bunun için öncelikle dünya ve güneşi düşünelim. Güneş yıldızı etrafında dönen dünya tıpki ötegezegenler gibi bir metod (dönüş) izler. Ancak bu dönüş süreleri farklıdır. Eğer gezegen hızlandığı vakit gezegen bulma tablosunda değer dalgalı fonksiyon once sabit sonra azalan daha sonra artan ise. Böylece gezegen olduğu ortaya çıkıyorsa. Başka ne söyleriz? O halde bir gezegenin yörüngesini hızlandırdığımız vakit güneşten yani yıldızdan hızlıca geçeceği için yıldız ışığına çok daha az maruz kalacağız demektir. Yörünge kütleçekimi demektir. Eğer kütle çekimi artarsa , yörünge ;yani iki cismin birbirlerine olan kütleçekimsel bağıntısı.(burada güneş ve dünya olur) yörünge hızı artacaktır ve karşıdaki yıldızdan ışık koparma azalacaktır. O halde SIR ISAAC NEWTON’un G.m1.m2 /r’2 formulünü kullanalım ve yeni bir şey türetelim.
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