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11 Learn all about CCDs; characterize our CCD Photometry and imaging, intro to spectroscopyDefinitions and opportunitiesPlanning and executing an observing runReducing and analyzing data Learn basics of IRAF as *one* image reduction and analysisprogram Draft a scientific paper of your work Must decide early in quarter if going for “W” credit (5 cr)FOCUSED OBJECTIVES:FOCUSED OBJECTIVES:2 Kinds of observations possible:Kinds of observations possible:cataclysmic variablescataclysmic variables3Kinds of observations possible: open cluster Kinds of observations possible: open cluster CMDCMD’’ssLarge angular size means shifting the telescope to get most of cluster.4Kinds of observations possible:Kinds of observations possible: globular cluster globular cluster CMDCMD’’ss25Kinds of observations possible: Kinds of observations possible: exoplanet exoplanet transitstransits6http://www.blackskies.org/sb2images.htmKinds of observations possible:Kinds of observations possible: planetary nebulaeplanetary nebulaeAngular sizesBrightness along an axis7Kinds of observations possible:Kinds of observations possible: galaxiesgalaxies8First: A bit of a review of Astro322First: A bit of a review of Astro322Then Fundamentals of PhotometryInstrumentsStar fieldsConsiderationsFiltersLimitations39Questions:Questions:1. What is it that we actually measure from a celestial object?2. What information about a star must we have before we can estimateits luminosity?3. If observing at optical wavelengths, what wavelength range wouldwe be considering?4. What does resolution depend upon?5. What does the number of photons we register in any given imagedepend upon?6. Approximate brightness ratio between 1st and 2nd magnitude star:7. Define the magnitude difference between 2 stars.8. What would the brightness of a star depend on?9. How would flux from very hot star differ from flux of very cool star?10Apparent magnitudeApparent magnitude of a star will depend on:Luminosity Distance (F is flux)Stuff in between it and us (extinction; reddening)! L = 4"r2#T4! F "1d2Definition of magnitude (visual wavelengths):! mv(A) " mv(B) = "2.5[log Iv(A) " log Iv(B)]Definition of “color” of a star:! m("1) # m("2) = #2.5[log I("1) # log I("2)]U # B = mU# mB, B # V = mB# mVV # R = mV# mR, R # I = mR# mI11Astronomical Photometry andAstronomical Photometry andImagingImagingHow to get from hereHow to get from hereto hereto hereOR here12Profile of a point-source (a star)Profile of a point-source (a star)starskybufferPoint spread function (PSF)4131. What is photometry anyway? How is it different fromimaging?2. What is the difference between differential photometryand absolute photometry?PhotometryPhotometry14Differential photometryDifferential photometry3. Let’s say we are monitoring a variable star and a single standard starin the field, doing differential photometry. Is this the best way todetermine the changes in magnitude of the variable star? Why orwhy not?4. Here’s a lovely star field covering about 0.9 x 0.6 degrees of the sky. Thefield of view using our 16” Meade LX200ACF and SBIG ST10XE camera isabout 12.6 x 8.5 arc minutes. Draw a square on any part of this image thatrepresents proportionally the amount of sky we can get on the CCD.155. Here’s a graph of the R magnitude error versusthe measured R magnitude of a set of stars.Why would we expect that the error wouldincrease the fainter the star is?6. What would be the main problem with doingdifferential photometry on the brightest starsseen in the image (even those in the uppercenter of the image)?7. A round star comes out as essentially a squarestar, with square pixels, to which you arefitting a round aperture. What are you goingto do with the signal registered in those partialpixels?16We always use filters in photometry. Originalfilter set was for a photometer, not CCDs.Telescopes may have different sets of filters(width and peak of band passes may differ,response may differ); may need to TRANSFORMmagnitudes to a standard system.517B V RB V RGetting the effective temperature of astar using broad band UBVRI filters 18A&A 451, 993-997 (2006) http://spiff.rit.edu/classes/phys445/lectures/colors/blink_j_c.html19 Medium-band photometry:Strömgren photometry – isolates specific parts of the spectrum of the star. Agreat system for determining metallicity of certain spectral classes of stars.2009. We will be taking images of celestial objects both with and without filters.If we take an image with no filter, and then use a filter for the next image of thesame object, would our second exposure need to be longer, shorter, or the samelength of time to get an equal amount of flux? Explain.08. We are usually after the luminosity of a star as that is an important intrinsiccharacteristic. We can measure its flux using our telescope and CCD and IRAF.How could we get its luminosity?10. Some of you may be observing globular or open clusters and producing acolor-magnitude diagram (we usually do V versus V – R). Using the magnitudeequation, show that the difference between the measured V magnitude and themeasured R magnitude is really a measure of the ratio of the fluxes.62111. On the topic of filters: Here is an image from the HST that used a series ofnarrow-band filters. We see an amazing amount of detail that contains a lot ofphysical information. Why not use narrow band filters for everything then?http://www.spacetelescope.org/static/projects/img/heic0205a_large.jpgAn example of a broad-band image.22Use of filters in imagingUse of filters in imaginghttp://www.spacetelescope.org/projects/fits_liberator/improc.html23Conditions that will affect our workConditions that will affect our work Interstellar dust Weather Sky brightness Airmass24Antares/Rho Ophiuchus RegionReddening(“de-bluing”)725Zhttp://calgary.rasc.ca/images/radec_celestial_equator.gifAIRMASS ≡ sec


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UW ASTR 480 - Lecture Notes

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