1 / 13

INAF – Osservatorio Astronomico di Brera Università degli Studi di Milano

Photometry of the galaxy NGC 6822 searching for Cepheid variable stars Alberto Chiodi's Graduation thesis Internal Supervisor: Laura Fracassini Pasinetti External Supervisor: Elio Antonello Merate – June 11 th 2004. INAF – Osservatorio Astronomico di Brera Università degli Studi di Milano.

oro
Download Presentation

INAF – Osservatorio Astronomico di Brera Università degli Studi di Milano

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. Photometry of the galaxy NGC 6822searching for Cepheid variable stars Alberto Chiodi's Graduation thesis Internal Supervisor: Laura Fracassini Pasinetti External Supervisor: Elio Antonello Merate – June 11th 2004 INAF – Osservatorio Astronomico di BreraUniversità degli Studi di Milano

  2. Topics • Cepheids • NGC 6822 • Photometry with IRAF • Future

  3. Variable stars: Cepheids • Instability strip • P-L relation

  4. Cepheids • Light curve of classical Cepheids • Fourier analysis • Comparison with teoretical models predictions Light curve of δ Cephei (period: 5.366d) Abscissa: phase, arbitrary units Ordinate: apparent magnitude (arbitrary zero point) (Cox, 1974)

  5. NGC 6822 (Wh band)

  6. White-light band • Images: 94x8=752 + bias and flat • Observing runs:

  7. Technical data: Importance: Proximity Sufficiently well resolved Comparison with other galaxies of the Local Group NGC 6822 or Barnard galaxy type: irregular dwarf Irr1(Sandage 1961) IB(s)m(De Vaucouleur et al 1964) first observation: 1886(Barnard) first images: 1906(Wolf) first classification: 1925(Hubble) Distance: ~500 Kpc

  8. Images reduction with IRAF packages • Header correction • Splitting images in chip (one chip at a time) • Trimming for overscan • Bias correction • Flat-field correction with normalized flat images • Problem of fringes in Wh-light images

  9. Defringing • Fringes as an additive phenomenon • Fringe images has to be normalized to the background sky • Fringes are subtracted from the original image

  10. Photometry analysis using DIGIPHOT-DAOPHOT packages • Problem of photometric Zero point correction of instrumental magnitudes • A star catalogue of the whole field of NGC6822 • Search for the variable stars • Construction • of the light- • curve • Classification • of the variables

  11. Future Merging with previous observations (Images of small parts of NGC6822 with the “Dutch” telescope (91 cm))

  12. Future Cepheids in NGC6822: • Hubble (1925): 11 • Kayser (1967): 13 • Humphreys (1980) and Schmidt & Spear (1989) : 40 • Antonello, E., Fugazza, D., Mantegazza, L., Stefanon, M., Covino, S., (2002): 53

  13. Future • Luca Fossati's graduation thesis IC1613 on the determination of the P-L relation from B,V,R,I WFI observations of the galaxy • Giovanni Grassi's graduation thesis on the other Wh-band images of NGC6822 obtained with the Dutch • Determination of the P-L relation of NGC6822 in B, V, R, I bands (using the light curves in the Wh-band, and just one or two points in B, V, R, I bands; extension of the Freedman method used for photographic light curves)

More Related