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IR Photometry Spectroscopy Crudest resolution : photometry spectral energy distribution (SED) U(0.37), B(0.44), V(0.55), R(0.64), Gound-based IR : I(0.80), J(1.25), H(1.65), K(2.2), L(3.5), M(4.8), N(10), Q(20 mm) 12, 25, 60, and 100 mm IRAS bands Dl/l ~< 0.01 : spectroscopy Ground-based IR Photometry Two regimes : JHKLM : shorter (sensitivity range of InSb detectors) NQ : longer (covered by bolometers and various photoconductive or photovoltaic detectors cooled to < 10 K) JHKLMNQ ; corresponds to a clear “window” of atmospheric transmission Window of Atm & Photometric bands, J. H, & K Johnson(1965) and Kitt Peak filters Window of Atm & Photometric band L Simons(1996) Window of Atm & Photometric band, M Simons(1996) Window of Atm & Photometric bands, N & Q Tokunaga(1999) Window of Atm & Photometric band, Q Simon et al(1972 IR Photometry Magnitude : ml =-2.5 log R +ZP , R= the instrumental response in the band, ZP = constant, zero-point Vega (bright A0V star) : zero mag at all wavelengths the average of (V- ml) for all A0V stars is zero for all bands Johnson et al(1966) : Vega at JHK =0.02 at each wavelength (also posses a circumstellar dust shell – beyond 20mm ;unsuitable for use as a standard at longer l ) Effective Wavelength Effective wavelength of a filter : leff = ∫ l S(l) h(l) dl / ∫ S(l)h(l) dl S(l) : transmission of the filter h(l) ; quantum efficiency of the detector Derivation of monochromatic flux densities from photometry The calibration of a standard star system is given as the flux corresponding to a zero mag star at the effective l of each band Because of the difficulties associated with conversion of mag. Into absolutely calibrated monochromatic fluxes, choose to discuss colors and magnitudes. Flux Correction Factor k Can construct correction tables for various assumed intrinsic spectral energy distributions with paticular filter transmission curves , the correction factor k, such that Fltrue(leff) = Flapparent (leff)/k for a particular monochromatic flux density distribution Fl(l) , can be calculated as follows : k={∫ Fl(l) S(l) dl / Fl(leff) } / {∫ Flstd(l) S(l) dl / Flstd(leff)} Factor k calculated for BB T 5000 3000 1000 800 600 400 300 Standard star is assumed to have a 10000 K BB spectral energy distribution . The detectors were modelled as a photon detector with responsivity proportional to l for JHKL and a bolometer for N. The JHKL filters were taken to be those of the SAAO(Carter, 1990) system with a hypothetical N- band from 8 to 14 mm. The precise values of the k-factors will differ from on photometric system to another kJ 0.99 0.96 1.03 1.14 1.42 2.62 5.48 kH 1.00 0.98 0.98 1.01 1.09 1.44 2.10 kK 1.00 0.99 0.98 0.98 1.00 1.09 1.25 kL kN 1.00 0.99 0.99 0.99 0.98 0.95 0.97 0.94 0.97 0.92 0.99 0.90 1.04 0.92 Isophotal wavelengths To find the l at which the simply-derived value for Fl is the correct one. The Isophotal wavelength of a filter and star combination is to be that quantity li which satisfies the relation Fl(li) ∫ S(l) dl = ∫ Fl S(l) dl = R Fl(l) is the monochromatic flux density from the star in units of W m-2sec-1mm-1, S(l) is the efficiency of the photometric system. R is proprotional to the response of the system( eg, the output voltage of the detector) IR Photometric bands Main problem ; the interference filters that define the bandpass cannot be reproduced with perfect accuracy Solve Having all filters in made the same batch manufacturing process and by observing the same set of standard stars. JHKLM Johnson(1962) : K (2.2mm) and L(3.6mm) Johnson (1964) : J (1.20 mm), K (2.20 mm) L (3.5 mm) and M(5.0 mm) Johnson et al 1968 : H (1.65 mm) Photovoltaic InSb L’ (3.8 mm) Ks (2.0-2.3 mm), K’ (1.9-2.3 mm) Window of Atm & Photometric bands, J. H, & K Johnson(1965) and Kitt Peak filters Window of Atm & Photometric band L Simons(1996) Window of Atm & Photometric band, M Simons(1996) Narrow-band CO and H2O photometry Sub-band of the K-band to isolate regions affected by CO (a narrow band filter centered at 2.36 mm) and water vapor( at 2.00 mm) A third narrow-band filter around 2.20 mm used for to define the unaffected continuum MIR, ground-based photometry Ge-doped bolometers, Doped Si arrays N-band (8 – 14 mm) : SAAO (1982) : cutoff 7.7mm , 80% to ~ 14 mm Rieke et al (1985) at 10 and 20 mm Thomas et al (1973) : narrower bands centered at 8.4 and 11.2 with broad-band N at 10.2 mm ESO : three narrow bands N1(8.4) , N2(9.69) and N3(12.9) Low and Rieke (1974) : bands at 11.5 and 13 mm Young et al (1994) ; narrow bands at 9.0 and 11.0 mm Q band region (17-27 mm) Poorly defined Standard Star Observations SAAO standard program of Carter(1990) Observing dwarf stars around A0 to set zero colors of V-K, J-H, H-K, and KL for dwarfs with B-V=0 Bessell and Brett (1988) ; set Vega’s all color zero. JHKL standard star programs Johnson (1964) ; adequate for a decade, not extend to the southern hemisphere Glass (1974) in Cape Town, Carter (1990) at Sutherland (SAAO), Engels et al (1981) and Bouchet et al (1991) at La Silla (ESO) Allen and Cragg (1983) at the Anglo-Australian Observatory (AAO) Elias et al (1982, 1983) at Caltech and Cerro Tololo Jones and Hyland (1982) & McGreger (1994) at Mount Stromlo (MSSSO) Faint standards UKIRT and related standards : a set of faint standards (8 < K < 14 mg) ; transformation eq to the CTIO-Caltech system (Casali and hawarden 1992) & extended by (Hunt et al 1998) Persson et al (1998) : 65 faint (10 < K < 12 )stars : J, H, K and Ks Intrinsic colors of dwarfs Besell and Brett(1988) Influence of molecular absorption on broad band colors Deviation of Giants in J-H, and H-K from the locus of BB : max at M2-M3 giants : due to the min. of the continuous b-f, f-f apsorption of H At < 3250 (M6) ;effect of H2O begin to dominate M-band at 4.8 mm strongly affected by CO L-M of giants < 0 at late M Color-color Dependance of J-K on metallicity d (J-K) ~ 0.15 for d (Z/Zo) = 1.5 : J-K becomes bluer for low metallicity Deviation from BB increases for low metallicities Absolute calibration I. Solar method : 1. observe G2 V stars’ V-J, V-K, V-L 2. take Vo= -26.74 . Derive apparent JKL mags of the sun 3. absolute energy distribution of the solar radiation taken from Allen(1963) II. BB comparision method : Walker (1969) 1.06, 1.13, 1.63 and 2.21 mm (detector PbS cell cooled to dry ice T) ; overall accuracy 10%, Selby et al (1983) narrower bands +-4% III. Comparison with stellar models : Cohen et al (1992) models of Vega and Sirius by Kurucz, normalized at measurements at 5556A, and use them to calculate isophotal wavelengths and monochromatic flux densities for various photometric systems. Absolute calibration Bessell, Castelli and Plez (1998) IRAS Photometry Van der Veen and Habing(1988) Bolometric Mag. apparent bolometric mag mbol = - 2.5 log ∫ Fl dl + C C = -18.980 in W m-2, -11.480 in erg cm-2 s-1 Absolute bolometric mag Mbol =4.74 -2.5 log (L/Lo) for solar constant 1360 W m-2 Lo = (3.826 +-0.008) * 1026 W Stellar effective Temperatures F = (f/2)2 s T4eff F ; tatal observed flux f : observed angular diameter Ridgway (1980) : spectral type vs T eff, V-K , and I(104)-L colors Di Benedetto (1993) ; tables of BC and Teff for stars of 1.42 < (V-K)o < 7.60 and luminosity classes I-V Infrared Flux method To get Teff : Blackwell and Shallis (1977) : a measurement of a star’s bolometric mag and a single near-IR continuum point determine Teff of it Megessier (1994) : shows ratio R =sT4 /Fl is sensitive to metallicity effect and gravity, besides temperature. the metallic lines reduce the UV flux, causing more energy to IR for a given effective T; order of 1 % Teff, different gravity may change it by half order 2% JHKL photometry of galaxies Galss (1984) : average colors of ordinary nearby galaxies Poggianti (1997) : k correction (changes of wavelength, bandwidth and intensity associated with reshift) in i filter Ki = -2.5 log (1+z) + 2.5 log ((∫ Fl (l) S(l) dl )/ (∫ Fl (l/(1+z)) S(l) dl)) S(l) : response of the filter and photometric system, z = red shift F(l) : observed flux density from the galaxy 1st term : arises from the narrowing of the filter passband in the restframe of the galaxy by a factor (1+z) 2nd term : allows for the fact that radiation seen by the observer at k-correction for galaxy photometry Typical K-corrections J-K -0.5z H-K -3.5z K 3.3z These quantities must be added to the observed quantity to get the rest-frame quantity : Frogel et al (1978) Approximately linear up to z=v/c = 0.2 Comprehensive tabel of K-correction : Poggianti(1997) K-correction Remember : a power law spectral distributiion undergoes Lorentz transformation without change of spectral index, and a BB spectral distribution transforms to another BB distribution , but with lower T. observed T Tobs =T(1-b cos q) (1-b2) -1/2 q : direcction of the motion to the line of sight b = v/c Photometric determination of redshifts Use of multicolor photometry Connolly et al (1995) ; galaxies out to z~0.8 and Bj < 22.5 using filters similar to the standard UBRI 4000 A break : cease to be useful ~ z=1 (it passes beyond I band) Work well for z> 2.2, where the Lyman limit(912A) enters the U-band Connolly et al(1997) : including J band to solve the problem of determining z for 1<z< 2 Effects of Star formation Colors of a galaxy bluer due to the presence of many hot, young stars. Galaxy evolution model : Leitherer et al (1996) Ellis 1997: star fomation peak ~ z=2 The slope of the relation between K mag and log (# of galaxies deg-2 mag-1) begin to turn over at K~ 19 Modelling galaxy Evolution Stellar populations : generated either initially, or contunously, according to certain conditions, such as metallicity, and mass function. Galaxy colors at high redshift Observed color of galaxies at high redshift : function of both evolution and redshift. Mobsher et al (1993) : at K band E/S0 and spiral galgxies have identical luminosity functions ;peak at K ~ 19 Star formation : Max at z =2 Homework The color indices of main sequence stars are given in the table. Find the colour temperature of the various spectral types (that is the temperature of the BB with the most similar spectrum in a given wavelength interval). For simplicity, represent each band by its central wavelength. Presentation 2 ESO Symposia: High Resolution Infrared Spectroscopy in Astronomy, 2005. © Springer-Verlag Berlin Heidelberg 2005 Spectral Properties of Brown Dwarfs and Hot Jupiters Derek Homeier et al ; p 465 Near-Infrared Spectroscopy of Deeply Embedded, Young Massive Stars Lex Kaper and Arjan Bik : p143 R=100,000 Mid-IR Spectroscopy of UCHII Regions: High Resolution is Worth it! Daniel. T. Jaffe : p 162 Outflows in Regions of Star Formation Ren´e Liseau : p185 High-Resolution Infrared Spectroscopy of Protoplanetary Disks John S. Carr : p 203 Active Stars and He I 10830 ˚A: the EUV Connection Jorge Sanz-Forcada and Andrea K. Dupree : p 256 Presentation 2 Chemical Abundances in the Galactic Bulge Livia Origlia and R. Michael Rich :p 347 The Infrared View on Red Supergiant Stars Eric Josselin and Bertrand Plez ; 405 Stellar Populations in the Galactic Bulge Mathias Schultheis, Bernhard Aringer, and Ariane Lan¸con : p 435 The Prospects of Searching for Planets of Brown Dwarfs with CRIRES Eike W. Guenther : p 487 Probing Thick Planetary Atmospheres with High Resolution Infrared Spectroscopy Catherine de Bergh and Bruno B´ezard ; p513 On the Variation of Cometary Polarisation Asoke K. Sen : p546