Podcasts about cepheids

Before you climb a ladder, you want to make sure all of its rungs are secure. And astronomers try to do the same thing – with the cosmic distance ladder. It’s a series of techniques that reveal the distances to objects that are farther and farther away. For it to work, all the rungs have to be secure. One of the first rungs on the ladder uses a class of stars called Cepheid variables – big stars that are nearing the end of life. They’re unstable, so they pulse in and out. The length of the pulses and other details reveal a Cepheid’s true brightness. From that, you can calculate the star’s distance. For this step to work, astronomers need to know all they can about Cepheids. But that’s not easy. In fact, they’re still debating the details on the closest and most famous Cepheid: Polaris, the pole star, which stands due north. We do know that Polaris consists of at least three stars. The Cepheid is the one that we see with our eyes alone. It has a close companion. The third member of the system is quite a ways from the other two. The system appears to be about 450 light-years away. And a recent study says the Cepheid is about five times the mass of the Sun. Its surface has some big dark and bright spots. Their motion suggests the star rotates once every four months. Even those details aren’t certain. So astronomers still have to do a lot of checking to make sure one of the rungs of the cosmic ladder is secure. Script by Damond Benningfield

We continue our discussion about the Hubble Constant and delve into a few other cosmic anomalies, including the assumption Albert Einstein made regarding the speed of light. And, somehow, we also ended up talking about Noah's flood and the Whopper Sand. You'll have to listen to the end to find out how that happened! Come and see how we think it all points to the glory and majesty of God. Dan's very short video on the whooper sand.   https://www.youtube.com/watch?v=7r9COYBra94   The following links are not meant to imply the ideas contained therein reflect those of Good Heavens! or Watchman Fellowship, Inc. All of these, with the exception of Danny Faulkner, are presented from a completely secular perspective of the universe Veritasium Video on the one-way speed of light problem. https://www.youtube.com/watch?v=pTn6Ewhb27k More in-depth on the Hubble Constant - Interview with Christian astronomer Dr. Danny Faulkner on the Hubble Constant. https://www.youtube.com/watch?v=zqUkhyxCbPE Cosmological constant (not the same as the Hubble constant, but related).  https://wmap.gsfc.nasa.gov/universe/uni_accel.html Hubble constant - two different ways to measure (from 2020).  https://www.scientificamerican.com/article/how-a-dispute-over-a-single-number-became-a-cosmological-crisis/ Three ways to measure Hubble constant.  https://news.uchicago.edu/explainer/hubble-constant-explained  Brian Keating short video about using magnetism to measure the Hubble constant  https://youtu.be/kBdtvURyJ8Q?si=-wlE-9D1emA-NP1- Dr. Becky most recent video on the crisis.  https://www.youtube.com/watch?v=yKmPJmaeP8A Adam Riese from the Space Telescope Science Institute who won the Nobel Prize in the late 90s for discovering the universe expansion was (allegedly) accelerating. His SH0ES team measured the Hubble constant at 74 km/s/mpsc, far above Wendy Freedman's 69.8 and the CMBR at 67.  https://www.youtube.com/watch?v=JmDszPExepc   Scientific American article on the HC from October 2023.  https://www.scientificamerican.com/article/a-possible-crisis-in-the-cosmos-could-lead-to-a-new-understanding-of-the-universe/   Wendy Freedman's initial project of measuring HC using the HST to measure Cepheids.  https://www.stsci.edu/stsci/meetings/shst2/freedmanw.html Historical background on the HC from STScI. (2020)  https://www.stsci.edu/contents/newsletters/2020-volume-37-issue-02/hubble-and-the-constant-the-next-and-the-next-generation Good Heavens! Is a production of Watchman Fellowship, Inc. For more information on our ministry and our sister podcast Apologetics Profile, visit Watchman.org today! Contact Wayne and Dan at  Psalm1968@gmail.com    Podbean enables our podcast to be on Apple Podcasts and other major podcast platforms.  To support Good Heavens! on Podbean as a patron, you can use the Podbean app, or go to https://patron.podbean.com/goodheavens.  This goes to Wayne Spencer. If you would like to give to the ministry of Watchman Fellowship or to Daniel Ray, you can donate at https://www.watchman.org/daniel. Donations to Watchman are tax deductible.

Probably the only thing that is constant about the Hubble Constant is that it keeps changing! What is it? Why is it such a hot topic in cosmology today and why are some even calling it a "crisis"? Come along with Wayne and Dan as they dive into the quest for the elusive magic number. What does it mean for cosmology and what might it all have to do with the way God made the universe? The following links are not meant to imply the ideas contained therein reflect those of Good Heavens! or Watchman Fellowship, Inc. All of these, with the exception of Danny Faulkner, are presented from a completely secular perspective of the universe More in-depth on the Hubble Constant - Interview with Christian astronomer Dr. Danny Faulkner on the Hubble Constant. https://www.youtube.com/watch?v=zqUkhyxCbPE Cosmological constant (not the same as the Hubble constant, but related).  https://wmap.gsfc.nasa.gov/universe/uni_accel.html Hubble constant - two different ways to measure.  https://www.scientificamerican.com/article/how-a-dispute-over-a-single-number-became-a-cosmological-crisis/ Three ways to measure Hubble constant. https://news.uchicago.edu/explainer/hubble-constant-explained  Brian Keating short video about using magnetism to measure the Hubble constant  https://youtu.be/kBdtvURyJ8Q?si=-wlE-9D1emA-NP1- Dr. Becky most recent video on the crisis. https://youtu.be/yKmPJmaeP8A?si=Wf6ajm4qGuC5CZX6 Adam Riese from the Space Telescope Science Institute who won the Nobel Prize in the late 90s for discovering the universe expansion was (allegedly) accelerating. His SH0ES team measured the Hubble constant at 74 km/s/mpsc, far above Wendy Freedman's 69.8 and the CMBR at 67. https://youtu.be/JmDszPExepc?si=03HqPi3RU5uRkSSl Technical  power point slides from Dr. Jo Dunkley on the PLANK CMBR data on the Hubble constant.  https://online.kitp.ucsb.edu/online/primocosmo13/dunkley/pdf/Dunkley_PrimoCosmo13_KITP.pdf Scientific American article on the HC from October 2023.  https://www.scientificamerican.com/article/a-possible-crisis-in-the-cosmos-could-lead-to-a-new-understanding-of-the-universe/ Wendy Freedman's initial project of measuring HC using the HST to measure Cepheids.  https://www.stsci.edu/stsci/meetings/shst2/freedmanw.html Historical background on the HC from STScI. (2020)  https://www.stsci.edu/contents/newsletters/2020-volume-37-issue-02/hubble-and-the-constant-the-next-and-the-next-generation Good Heavens! Is a production of Watchman Fellowship, Inc. For more information on our ministry and our sister podcast Apologetics Profile, visit Watchman.org today! Contact Wayne and Dan!    Psalm1968@gmail.com    Podbean enables our podcast to be on Apple Podcasts and other major podcast platforms.  To support Good Heavens! on Podbean as a patron, you can use the Podbean app, or go to https://patron.podbean.com/goodheavens.  This goes to Wayne Spencer. If you would like to give to the ministry of Watchman Fellowship or to Daniel Ray, you can donate at https://www.watchman.org/daniel. Donations to Watchman are tax deductible.

We know today that our universe is huge and that it contains more than a hundred billion galaxies! But this view of the universe is only a hundred years old. What is fascinating is that a particular type of star, called Cepheids, is primarily responsible for the change of our view. In this episode of Kainaati Gup Shup, astrophysicist Salman Hameed discuss why Cepheids played such a central role in this episode of Kainaati Gup Shup. 

It's not often that a single star transforms our view of the universe. But it happened with a star that was photographed 100 years ago tonight. The star proved that there's more to the universe than just the Milky Way Galaxy — much more. The star is known today as M31-V1. It's in M31, the Andromeda Galaxy. A century ago, M31 was called the Andromeda Nebula. Many astronomers thought it was a mote of matter inside the Milky Way. Others thought it was a separate galaxy — an “island universe” of billions of stars. On the night of October 5th of 1923, Edwin Hubble snapped a picture of a small segment of M31. He identified three stars that had grown much brighter since the last time he looked at them. Follow-up observations showed that one star's brightness changed from night to night. That star was a Cepheid — a supergiant star that's unstable. It pulses in and out like a beating heart. The duration of the pulses revealed the star's true brightness. And from that, Hubble calculated its distance — a million light-years. Studies of other Cepheids confirmed the distance. So M31 had to be well beyond the Milky Way — vastly expanding our understanding of the universe. Modern observations put the distance to M31 at two-and-a-half million light-years. And the galaxy is visible to the unaided eye. Under dark skies, it looks like a faint smudge of light, in the north-northeast at nightfall.  Script by Damond Benningfield Support McDonald Observatory

Understanding the future of the universe requires peering into the past. How quickly the universe is expanding has been an active area of science since the 1920s, with several prizes and breakthroughs. Each time we get new or more accurate measurements it forces scientists to re-evaluate the assumptions and formulas. These breakthroughs then need to be confirmed with follow up studies. The measurement of Hubble's constant using supernova won a Nobel Prize in 2011, and new gravitational lensing measurements have provided extra confirmation to those numbers. Dark matter can influence a lot in our universe, but measuring it is difficult but using lensing techniques a more accurate measurement can be derived. Mauricio Cruz Reyes, Richard I. Anderson. A 0.9% calibration of the Galactic Cepheid luminosity scale based on Gaia DR3 data of open clusters and Cepheids. Astronomy & Astrophysics, 2023; 672: A85 DOI: 10.1051/0004-6361/202244775 Princeton University. (2023, April 7). How to see the invisible: Using the dark matter distribution to test our cosmological model. ScienceDaily. Retrieved April 14, 2023 from www.sciencedaily.com/releases/2023/04/230407215847.htm

Period variation of the classical Cepheid SV Vulpeculae over a century 1913-2022 by Guy Boistel. on Wednesday 30 November This study analyzes 338 new times of visual, CCD, photoelectric and photographic maxima of the classical Cepheid SV Vul. The corresponding observations were made between 1913 and 2022. On this new and large observational basis, the period variations of this star of major astrophysical interest are re-visited. Without contradicting the theory or previous studies, we show that visual observations are important for a long-term monitoring of the period variations of well-selected bright Cepheids. This study establishes the period rate of change of SV Vul at -250 s/yr. Its period is currently shorter than 45 days. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.16025v1

Period variation of the classical Cepheid SV Vulpeculae over a century 1913-2022 by Guy Boistel. on Tuesday 29 November This study analyzes 338 new times of visual, CCD, photoelectric and photographic maxima of the classical Cepheid SV Vul. The corresponding observations were made between 1913 and 2022. On this new and large observational basis, the period variations of this star of major astrophysical interest are re-visited. Without contradicting the theory or previous studies, we show that visual observations are important for a long-term monitoring of the period variations of well-selected bright Cepheids. This study establishes the period rate of change of SV Vul at -250 s/yr. Its period is currently shorter than 45 days. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.16025v1

Period Change Rates of Large Magellanic Cloud Cepheids using MESA by F. Espinoza-Arancibia et al. on Thursday 22 September Pulsating stars, such as Cepheids and RR Lyrae, offer us a window to measure and study changes due to stellar evolution. In this work, we study the former by calculating a set of evolutionary tracks of stars with an initial mass of 4 to 7 $M_odot$, varying the initial rotation rate and metallicity, using the stellar evolution code Modules for Experiments in Stellar Astrophysics (MESA). Using Radial Stellar Pulsations (RSP), a recently added functionality of MESA, we obtained theoretical instability strip (IS) edges and linear periods for the radial fundamental mode. Period-age, period-age-temperature, period-luminosity, and period-luminosity-temperature relationships were derived for three rotation rates and metallicities, showing a dependence on crossing number, position in the IS, rotation, and metallicity. We calculated period change rates (PCRs) based on the linear periods from RSP. We compared our models with literature results using the Geneva code, and found large differences, as expected due to the different implementations of rotation between codes. In addition, we compared our theoretical PCRs with those measured in our recent work for Large Magellanic Cloud Cepheids. We found good overall agreement, even though our models do not reach the short-period regime exhibited by the empirical data. Implementations of physical processes not yet included in our models, such as pulsation-driven mass loss, an improved treatment of convection that may lead to a better description of the instability strip edges, as well as consideration of a wider initial mass range, could all help improve the agreement with the observed PCRs. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.10609v1

A reanalysis of the latest SH0ES data for H 0 : Effects of new degrees of freedom on the Hubble tension by Leandros Perivolaropoulos et al. on Tuesday 20 September We reanalyze the recently released SH0ES data for the determination of $H_0$. We focus on testing the homogeneity of the Cepheid+SnIa sample and the robustness of the results in the presence of new degrees of freedom in the modeling of Cepheids and SnIa. We thus focus on the four modeling parameters of the analysis: the fiducial luminosity of SnIa $M_B$ and Cepheids $M_W$ and the two parameters ($b_W$ and $Z_W$) standardizing Cepheid luminosities with period and metallicity. After reproducing the SH0ES baseline model results, we allow for a transition of the value of any one of these parameters at a given distance $D_c$ or cosmic time $t_c$ thus adding a single degree of freedom in the analysis. When the SnIa absolute magnitude $M_B$ is allowed to have a transition at $D_csimeq 50Mpc$ (about $160Myrs$ ago), the best fit value of the Hubble parameter drops from $H_{0}=73.04pm1.04,km,s^{-1},Mpc^{-1}$ to $H_0=67.32pm 4.64, km,s^{-1},Mpc^{-1}$ in full consistency with the Planck value. Also, the best fit SnIa absolute magnitude $M_B^>$ for $D>D_c$ drops to the Planck inverse distance ladder value $M_{B}^>=-19.43pm 0.15$ while the low distance best fit $M_B^

A First Look at Cepheids in a SN Ia Host with JWST by Wenlong Yuan et al. on Tuesday 20 September We report the first look at extragalactic Cepheid variables with the James Webb Space Telescope, obtained from a serendipitous (to this purpose) observation of NGC 1365, host of an SN Ia (SN 2012fr), a calibration path used to measure the Hubble constant. As expected, the high-resolution observations with NIRCam through F200W show better source separation from line-of-sight companions than HST images at similar near-infrared wavelengths, the spectral region that has been used to mitigate the impact of host dust on distance measurements. Using the standard star P330E as a zeropoint and PSF reference, we photometered 31 previously-known Cepheids in the JWST field, spanning 1.15 < log P < 1.75 including 24 Cepheids in the longer period interval of 1.35 < log P < 1.75. We compared the resultant Period-Luminosity relations to that of 49 Cepheids in the full period range including 38 in the longer period range observed with WFC3/IR on HST and transformed to the JWST photometric system (F200W, Vega). The P-L relations measured with the two space telescopes are in good agreement, with intercepts (at log P=1) of 25.74+/-0.04 and 25.72+-0.05 for HST and JWST, respectively. Our baseline result comes from the longer period range where the Cepheids have higher signal-to-noise ratios where we find 25.75+-0.05 and 25.75+-0.06 mag for HST and JWST, respectively. We find good consistency between this first JWST measurement and HST, and no evidence that HST Cepheid photometry is "biased bright" at the ~0.2 mag level that would be needed to mitigate the Hubble Tension, though comparisons from more SN hosts are warranted and anticipated. We expect future JWST observations to surpass these in quality as they will be optimized for measuring Cepheids. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.09101v1

A reanalysis of the latest SH0ES data for H 0 : Effects of new degrees of freedom on the Hubble tension by Leandros Perivolaropoulos et al. on Tuesday 20 September We reanalyze the recently released SH0ES data for the determination of $H_0$. We focus on testing the homogeneity of the Cepheid+SnIa sample and the robustness of the results in the presence of new degrees of freedom in the modeling of Cepheids and SnIa. We thus focus on the four modeling parameters of the analysis: the fiducial luminosity of SnIa $M_B$ and Cepheids $M_W$ and the two parameters ($b_W$ and $Z_W$) standardizing Cepheid luminosities with period and metallicity. After reproducing the SH0ES baseline model results, we allow for a transition of the value of any one of these parameters at a given distance $D_c$ or cosmic time $t_c$ thus adding a single degree of freedom in the analysis. When the SnIa absolute magnitude $M_B$ is allowed to have a transition at $D_csimeq 50Mpc$ (about $160Myrs$ ago), the best fit value of the Hubble parameter drops from $H_{0}=73.04pm1.04,km,s^{-1},Mpc^{-1}$ to $H_0=67.32pm 4.64, km,s^{-1},Mpc^{-1}$ in full consistency with the Planck value. Also, the best fit SnIa absolute magnitude $M_B^>$ for $D>D_c$ drops to the Planck inverse distance ladder value $M_{B}^>=-19.43pm 0.15$ while the low distance best fit $M_B^

A First Look at Cepheids in a SN Ia Host with JWST by Wenlong Yuan et al. on Tuesday 20 September We report the first look at extragalactic Cepheid variables with the James Webb Space Telescope, obtained from a serendipitous (to this purpose) observation of NGC 1365, host of an SN Ia (SN 2012fr), a calibration path used to measure the Hubble constant. As expected, the high-resolution observations with NIRCam through F200W show better source separation from line-of-sight companions than HST images at similar near-infrared wavelengths, the spectral region that has been used to mitigate the impact of host dust on distance measurements. Using the standard star P330E as a zeropoint and PSF reference, we photometered 31 previously-known Cepheids in the JWST field, spanning 1.15 < log P < 1.75 including 24 Cepheids in the longer period interval of 1.35 < log P < 1.75. We compared the resultant Period-Luminosity relations to that of 49 Cepheids in the full period range including 38 in the longer period range observed with WFC3/IR on HST and transformed to the JWST photometric system (F200W, Vega). The P-L relations measured with the two space telescopes are in good agreement, with intercepts (at log P=1) of 25.74+/-0.04 and 25.72+-0.05 for HST and JWST, respectively. Our baseline result comes from the longer period range where the Cepheids have higher signal-to-noise ratios where we find 25.75+-0.05 and 25.75+-0.06 mag for HST and JWST, respectively. We find good consistency between this first JWST measurement and HST, and no evidence that HST Cepheid photometry is "biased bright" at the ~0.2 mag level that would be needed to mitigate the Hubble Tension, though comparisons from more SN hosts are warranted and anticipated. We expect future JWST observations to surpass these in quality as they will be optimized for measuring Cepheids. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.09101v1

No-go guide for late-time solutions to the Hubble tension: Matter perturbations by Rong-Gen Cai et al. on Monday 19 September The Hubble tension seems to be a crisis with $sim5sigma$ discrepancy between the most recent local distance ladder measurement from type Ia supernovae calibrated by Cepheids and the global fitting constraint from the cosmic microwave background data. To narrow down the possible late-time solutions to the Hubble tension, we have used in a recent study [Phys. Rev. D 105, L021301 (2022)] an improved inverse distance ladder method calibrated by the absolute measurements of the Hubble expansion rate at high redshifts from the cosmic chronometer data, and found no appealing evidence for new physics at the late time beyond the $Lambda$CDM model characterized by a parametrization based on the cosmic age. In this paper, we further investigate the perspective of this improved inverse distance ladder method by including the late-time matter perturbation growth data. Independent of the dataset choices, model parametrizations, and diagnostic quantities ($S_8$ and $S_{12}$), the new physics at the late time beyond the $Lambda$CDM model is strongly disfavored so that the previous late-time no-go guide for the Hubble tension is further strengthened. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2202.12214v3

Machine Learning the Hubble Constant by Carlos Bengaly et al. on Monday 19 September Local measurements of the Hubble constant ($H_0$) based on Cepheids e Type Ia supernova differ by $approx 5 sigma$ from the estimated value of $H_0$ from Planck CMB observations under $Lambda$CDM assumptions. In order to better understand this $H_0$ tension, the comparison of different methods of analysis will be fundamental to interpret the data sets provided by the next generation of surveys. In this paper, we deploy machine learning algorithms to measure the $H_0$ through a regression analysis on synthetic data of the expansion rate assuming different values of redshift and different levels of uncertainty. We compare the performance of different algorithms as Extra-Trees, Artificial Neural Network, Extreme Gradient Boosting, Support Vector Machines, and we find that the Support Vector Machine exhibits the best performance in terms of bias-variance tradeoff, showing itself a competitive cross-check to non-supervised regression methods such as Gaussian Processes. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.09017v1

Cepheid Metallicity in the Leavitt Law C- MetaLL survey: II High-resolution spectroscopy of the most metal poor Galactic Cepheids by E. Trentin et al. on Thursday 08 September Classical Cepheids (DCEPs) are the first fundamental step in the calibration of the cosmological distance ladder. Furthermore, they represent powerful tracers in the context of Galactic studies. We have collected high-resolution spectroscopy with UVES@VLT for a sample of 65 DCEPs. The majority of them are the faintest DCEPs ever observed in the Milky Way. For each target, we derived accurate atmospheric parameters, radial velocities, and abundances for 24 different species. The resulting iron abundances range between +0.3 and $-$1.1 dex with the bulk of stars at [Fe/H]$sim-0.5$ dex. Our sample includes the most metal-poor DCEPs observed so far with high-resolution spectroscopy. We complement our sample with literature data obtaining a complete sample of 637 DCEPs and use Gaia Early Data Release 3 (EDR3) photometry to determine the distance of the DCEPs from the Period-Wesenheit-Metallicity relation. Our more external data trace the Outer arm (at Galactocentric radius ($R_{GC})sim$16--18 kpc) which appears significantly warped. We investigate the metallicity gradient of the Galactic disc using this large sample, finding a slope of $-0.060 pm 0.002$ dex kpc$^{-1}$, in very good agreement with previous results based both on DCEPs and open clusters. We also report a possible break in the gradient at $R_{GC}$=9.25 kpc with slopes of $-0.063 pm 0.007$ and $-0.079 pm 0.003$ dex kpc$^{-1}$ for the inner and outer sample, respectively. The two slopes differ by more than 1 $sigma$. A more homogeneous and extended DCEPs sample is needed to further test the plausibility of such a break. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.03792v1

Tracing the Milky Way warp and spiral arms with classical Cepheids by B. Lemasle et al. on Wednesday 07 September Mapping the Galactic spiral structure is a difficult task since the Sun is located in the Galactic plane and because of dust extinction. For these reasons, molecular masers in radio wavelengths have been used with great success to trace the Milky Way spiral arms. Recently, Gaia parallaxes have helped in investigating the spiral structure in the Solar extended neighborhood. In this paper, we propose to determine the location of the spiral arms using Cepheids since they are bright, young supergiants with accurate distances (they are the first ladder of the extragalactic distance scale). They can be observed at very large distances; therefore, we need to take the Galactic warp into account. Thanks to updated mid-infrared photometry and to the most complete catalog of Galactic Cepheids, we derived the parameters of the warp using a robust regression method. Using a clustering algorithm, we identified groups of Cepheids after having corrected their Galactocentric distances from the (small) effects of the warp. We derived new parameters for the Galactic warp, and we show that the warp cannot be responsible for the increased dispersion of abundance gradients in the outer disk reported in previous studies. We show that Cepheids can be used to trace spiral arms, even at large distances from the Sun. The groups we identify are consistent with previous studies explicitly deriving the position of spiral arms using young tracers (masers, OB(A) stars) or mapping overdensities of upper main-sequence stars in the Solar neighborhood thanks to Gaia data. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.02731v1

Variable star classification with a Multiple-Input Neural Network by T. Szklenár et al. on Tuesday 06 September In this experiment, we created a Multiple-Input Neural Network, consisting of Convolutional and Multi-layer Neural Networks. With this setup the selected highest-performing neural network was able to distinguish variable stars based on the visual characteristics of their light curves, while taking also into account additional numerical information (e.g. period, reddening-free brightness) to differentiate visually similar light curves. The network was trained and tested on OGLE-III data using all OGLE-III observation fields, phase-folded light curves and period data. The neural network yielded accuracies of 89--99% for most of the main classes (Cepheids, $delta$ Scutis, eclipsing binaries, RR Lyrae stars, Type-II Cepheids), only the first-overtone Anomalous Cepheids had an accuracy of 45%. To counteract the large confusion between the first-overtone Anomalous Cepheids and the RRab stars we added the reddening-free brightness as a new input and only stars from the LMC field were retained to have a fixed distance. With this change we improved the neural network's result for the first-overtone Anomalous Cepheids to almost 80%. Overall, the Multiple-input Neural Network method developed by our team is a promising alternative to existing classification methods. arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2209.02310v1

NGC 3621 is one of a few galaxies where its distance has been measured with high accuracy using Cepheids and other stars with known brightness, thus making it very important for measuring the expansion of the universe.

First in a two-part series about stars and how we classify them. Variables are a very specific kind of star that have a regular variation in brightness, like a heartbeat. They were first categorized and analyzed by Henrietta Swan Leavitt at the turn of the 20th century at Harvard University, along with other women computers at the time. Leavitt noticed variable stars in the Magellanic Clouds and came up with her luminosity law, where the pulse rates of Cepheid variable stars are proportional to their luminosity—the brighter they are, the greater their period is. This law helped estimate interstellar and intergalactic distances. Cepheids and other kinds of variable stars have helped astronomers map out the size of our galaxy, the spaces between celestial objects, and the distance to the outer reaches of our universe.

Astronomers using the VISTA telescope at ESO’s Paranal Observatory have discovered a previously unknown component of the Milky Way. By mapping out the locations of a class of stars that vary in brightness called Cepheids, a disc of young stars buried behind thick dust clouds in the central bulge has been found. Support this podcast: Drive with Uber and make real, serious money! I use Uber when I need rides when I travel and the drivers I talk with love driving on their own schedule. http://ubr.to/1O3MOV2 https://www.patreon.com/spaceindustrynews --- Support this podcast: https://anchor.fm/space-news/support

Transcript: The fact that quasars are at large distances and have huge luminosities depends on the cosmological interpretation of their redshift. There are some crucial distinctions between galaxies and quasars as far as redshift goes. For galaxies they follow a Hubble relation where distance indicators such as Cepheids within the galaxies or supernovae in more distant galaxies reliably indicate distance and are correlated well with redshift. Quasars have no property that correlates well with redshift. The luminosity varies by a factor of thousands between different objects, and the light from the quasar is variable on timescales of weeks, months, and years. So the redshift itself is used as a distance indicator. In many cases the redshift is high enough that the host galaxy cannot be seen. Quasar redshifts begin at a few tenths, and beyond a redshift of a half the host galaxy is usually not visible. The highest quasar redshifts are six or seven, an age when the universe was only ten percent of its current age and seven times smaller than it is now.

Transcript: Cepheid variables are luminous stars with variations in a range of periods of one to fifty days. The physics of their pulsation is well understood, and empirically for stars with well measured distance by parallax, there’s a well determined relationship between the period of the pulsation and the luminosity of the star. More luminous Cepheids have longer periods. Astronomers therefore isolate Cepheids in a distant cluster by taking images over a period of several months to identify the variable stars and measure their periods. The period then leads to a prediction of the luminosity. That is combined with the apparent brightness to yield a distance. The Cepheid distance measurement technique is among the most accurate in astronomy with a precision of ten percent.

Transcript: When Magellan traveled round the world in the early sixteenth century, there was no bright star near the southern celestial pole, so for navigation he used two glowing patches of light which became known the Magellanic Clouds. But of course, they must have been known throughout prehistory and were undoubtedly the subject of myth and legend. They’re companions to the Milky Way galaxies, and they are extremely important in astronomy because their stellar nurseries are close enough to get a detailed view and identify individual examples of rare stellar populations such as RR Lyraes, Cepheids, novae, planetary nebulae, and more exotic variable stars.

Transcript: When Magellan traveled round the world in the early sixteenth century, there was no bright star near the southern celestial pole, so for navigation he used two glowing patches of light which became known the Magellanic Clouds. But of course, they must have been known throughout prehistory and were undoubtedly the subject of myth and legend. They’re companions to the Milky Way galaxies, and they are extremely important in astronomy because their stellar nurseries are close enough to get a detailed view and identify individual examples of rare stellar populations such as RR Lyraes, Cepheids, novae, planetary nebulae, and more exotic variable stars.

Transcript: Hubble’s use of Cepheid variables to measure the distance to the Andromeda nebula is sufficiently important in the history of astronomy to study his logic carefully. He started by taking sequential observations on photographic plates over a period of months allowing him to identify variable stars in the Andromeda nebula. He knew that there was a universal period-luminosity relationship for Cepheid variables in the Milky Way. He then identified Cepheids with the same periods near the Sun whose distances were measured by other means and in the Andromeda nebula. These therefore have the same luminosity or absolute magnitude. He measured the apparent brightness difference between the Cepheid variables and the ones in the Milky Way. They were typically a million times fainter. By the inverse square law the M31 Cepheids must be the square root of a million, a thousand times further away. So if the local Cepheid is at a distance of two thousand light years the M31 Cepheid must be a thousand times further away, two million light years.

Transcript: Beyond a distance of about twenty megaparsecs, or sixty or seventy million lightyears, it becomes difficult to use individual stars as distance indicators. Cepheid variables are hopelessly blurred in the summed light of billions of stars in the distant galaxy, and even supernovae, which indeed can be seen above the light of an individual galaxy, may be imbedded in dusty regions. In addition, there are multiple types of supernovae, and with out high quality spectroscopic information it’s not always easy to pick the one that is the precise and reliable distance indicator. Thus astronomers use global properties of galaxies to estimate distances which is okay as long as they are calibrated by a technique with well understood physics in the nearby regions, such as Cepheids or supernovae. Unfortunately the two most obvious properties of galaxies are poor distance indicators. Apparent brightness is a bad estimator of distance because galaxies come in such a wide range of luminosities, and apparent size is a bad estimator of distances because galaxies range by over two orders of magnitude in their true physical sizes.

Transcript: In the nearby universe astronomers primarily use stars as distance indicators. Cepheid variables which were classically used by Hubble to demonstrate the distance to the nebulae and the universal expansion are still used. As luminous stars with well understood physics they can be found locally in the Milky Way where their distances are tethered by parallax and main sequence fitting, but they are bright enough to be observed out to distances of twenty megaparsecs or over fifty million lightyears, a region which encompasses dozens of galaxies. Beyond this distance observation of Cepheids is limited by the crowding of the stellar fields and by their faintness. Supernovae can be observed to much larger distances, easily to five megaparsecs, and individual examples have been found two or three times further than this. However, they are rare; only one supernova occurs in every fifty years per galaxy on average. So they cannot reliably be found in any particular galaxy, and there hasn’t been a supernova in the Milky Way to tether the distance indicator for several centuries.

The aim of this thesis is to assess the effect of the metallicity on the Cepheid Period-Luminosity (PL) relation. The novelty of the approach adopted in this project consists in the homogeneous analysis of a large sample of Cepheids (72) observed in three galaxies (the Milky Way, the Large Magellanic Cloud and the Small Magellanic Cloud), spanning a factor of ten in metallicity. This allows us to explore the effect of the metallicity on the PL relation in a wide range and to study the gas enrichment histories of three different galaxies. To fulfil this goal, firstly, we have selected a sample of Cepheids for which distances and accurate photometry are available in the literature and we have collected high-resolution, high signal-to-noise spectra of these stars, using the highly advanced facilities of the European Southern Observatory in Chile. Secondly, we have directly measured iron and alpha-elements (O, Na, Mg, Al, Si, Ca, Ti) abundances of our sample from these spectra. We have compared our iron abundances with studies on Galactic and Magellanic Cepheids and found a good agreement for the average values and for the individual stars in common. We have then made a broader comparison with results for the Magellanic Clouds from the analysis of F and K non-variable supergiants (they have ages and temperatures similar to Cepheid stars) and of B stars, which are progenitors of Cepheids, and found a good agreement. Cepheids do not show any peculiar differences with these two other population of stars, this indicate that, during this evolutionary stage, there are no changes of the original iron content of the gas from which they were formed. We have then studied the trends of the individual alpha-elements abundance ratios relative to iron as a function of the iron content of our programme star. We can draw some preliminary conclusion considering oxygen, silicon and calcium as the most reliable indicators among the alpha-elements we have analysed. The trends of the abundance ratios of O, Si and Ca are in fairly good agreement with observational studies on Cepheids and on different kinds of stellar populations in the Galaxy and the Magellanic Clouds. The elemental abundances we have determined were used to investigate the effect of metallicity on the PL relation in the V and K bands, in order to check if there is a change of the effect as wavelength increases. We note different behaviours in the two bands. The metallicity has an effect in the V band in the sense that metal-rich Cepheids are fainter than metal-poor ones, while it does not have any effects in the K band. Thus, to safely measure the distances of galaxies, one can use the PL relation in the infrared bands (namely K), so as to minimise the effect of the metallicity. Using the K band has the additional advantage of reducing the effects of the interstellar extinction to the level of other systematic and random errors.