1 / 33

1qa1qa31qa1qa

1qa1qa31qa1qa. 1qaz1qaz1qa1qa. He+ is ionized to He++ within the partial-ionization layer near the surface of the star whenever T > 40,000K. The outer layers contracts and reheat to 40,000K, and the ionization cycle begins again.

bud
Download Presentation

1qa1qa31qa1qa

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 1qa1qa31qa1qa 1qaz1qaz1qa1qa

  2. He+ is ionized to He++ within the partial-ionization layer near the surface of the star whenever T > 40,000K.

  3. The outer layers contracts and reheat to 40,000K, and the ionization cycle begins again. This sort of stuff happens all the time within stars – including the Sun – wherever the internal temperature crosses the ionization threshold of important elements. Along the instability strip, however, the period for He++ ionization cycling is approximately equal to the overall acoustic oscillation period within the star, and so these fluctuations become greatly amplified and readily detectable. - - - - When this happens, the opacity of the layer goes up due to the increased number of free electrons.

  4. The greater opacity drives up the temperature and pressure gradients across the partial-ionization layer, which physically expands outward and cools.

  5. As the layer cools, He++ recombines with free electrons to form He+, driving the opacity back down and decreasing the temperature and pressure gradient.

  6. The outer layers contracts and reheat to 40,000K, and the ionization cycle begins again.

  7. All stars are somewhat variable, even the Sun. These stars get hundreds of times brighter and dimmer, over the course of just a few hours to days. Variable stars, like candles or light bulbs flickering, aren’t variable for MOST of their existence. The extreme swings in brightness are a “short” phase during an otherwise more ordinary story.

  8. RR Lyrae type stars are made almost exclusively of atoms created in the Big Bang. They were made at a different era of the universe than our sun. Globular cluster M15

  9. RRc type variable star light curve (RRBoo) http://www.astronet.ru/db/varstars/msg/1226033 RRab stars have less symmetric light curves

  10. So it’s variable. So what ? • The period of these stars relates to mass • Their mass relates to their INTRINSIC brightness • Comparing the INTRINSIC brightness to the OBSERVED brightness shows how far away the star is • We can make a map.

  11. Harvard Astronomer Henrietta Leavitt showed this in the 1920’s. • Edwin Hubble used Leavitt’s “yardstick” to show the Andromeda “Nebula” lay far, far, faaaaaaar beyond the stars in the Milky Way. • Red Shift -> expanding universe • Sea of Galaxies

  12. http://www.atlasoftheuniverse.com/sattelit.html

  13. http://www.astro.uu.se/~ns/mwsat.html

  14. http://www.daviddarling.info/images/Sagittarius_Dwarf_Elliptical.jpghttp://www.daviddarling.info/images/Sagittarius_Dwarf_Elliptical.jpg

  15. http://www.astro.utu.fi/~cflynn/galdyn/Milkyway.s.gif

  16. http://www.solstation.com/x-objects/sag2cann.jpg

  17. Artist's rendition of the path of satellite galaxy Complex H (in red) in relation to the orbit of the Sun (in yellow) about the center of the Milky Way Galaxy. The outer layers of Complex H are being stripped away by its interaction with the Milky Way. The hydrogen atmosphere (in blue) is shown surrounding the visible portion (in white) of the Galaxy. CREDIT: Lockman, Smiley, Saxton; NRAO/AUI

  18. Image of the stellar tidal stream surrounding the spiral galaxy NGC 5907 obtained with an amateur robotic telescope in the mountains of New Mexico. (Credit: R. Jay Gabany)

  19. Manastash Ridge Observatory

  20. 30 inch Boller-Chivens reflector Equatorial mount Filter slide CCD camera 1 megapixel Thermoelectrically cooled to -60 degrees C

  21. Raw Data from a set of 8 mosaiced CCDs

  22. Bias images before and after correction for Cosmic Ray strikes

  23. Raw data with bias removed

  24. Sky flats

  25. Data with bias correction and Sky flats divided out

  26. Before me: • Compare new star catalogs with older ones to identify variable star candidates • Create candidate list: observable in summer, highly grouped, 15th to 18th magnitude

  27. Me: • Observatory time ~ 25 to 30 observations of ~ 60 candidate stars • Computer Lab time - Bias & flat subtraction - Labeling of target star - Comparison of target star pixels with fixed magnitude field stars - Fitting of variations to standard RR light curves • Accept or reject as RR Lyrae type star.

  28. After me: • Place star into growing map of Milky Way • Make velocity measurements (doppler shift from spectrography). • Make composition measurements (spectrography) • Use distance, velocity, & composition to associate RR stars into groups or streams within but distinct from Milky Way stars. • Use streams to infer evolution of Milky Way and galaxies in general. • Investigate gravitational attractions in Milky Way (including those from dark matter)

  29. With appreciation: • Murdock Foundation • Chris Laws: mentor & Duke of MRO • Julie Lutz: Queen of UW Astronomy • Gabriella Gutierrez: Princess of my Heart

More Related