The DDO photometric system1 It was developed at the David Dunlap Observatory near Toronto by McClure...

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The DDO photometric system The DDO photometric system 1 The DDO photometric system The DDO photometric system It was developed at It was developed at the the D D avid avid D D unlap unlap O O bservatory near bservatory near Toronto by McClure & Toronto by McClure & van den Bergh (1968) van den Bergh (1968) Intermediate band Intermediate band system, filter system, filter defined: 48 (at defined: 48 (at λ4886), 45 (at λ4517), λ4886), 45 (at λ4517), 42 (at λ4257), 41 (at 42 (at λ4257), 41 (at λ4166), 38 λ4166), 38 b (at λ3815) (at λ3815) and 35 (at λ3460) and 35 (at λ3460)
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Transcript of The DDO photometric system1 It was developed at the David Dunlap Observatory near Toronto by McClure...

The DDO photometric systemThe DDO photometric system 11

The DDO photometric The DDO photometric systemsystem

It was developed at the It was developed at the DDavid avid DDunlap unlap OObservatory near bservatory near Toronto by McClure & Toronto by McClure & van den Bergh (1968)van den Bergh (1968)

Intermediate band Intermediate band system, filter defined: system, filter defined: 48 (at 48 (at λ4886), 45 (at λ4886), 45 (at λ4517), 42 (at λ4257), λ4517), 42 (at λ4257), 41 (at λ4166), 3841 (at λ4166), 38bb (at (at λ3815) and 35 (at λ3815) and 35 (at λ3460)λ3460)

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The DDO photometric The DDO photometric systemsystem

210 stars, 70 star clusters and 56 galaxies were 210 stars, 70 star clusters and 56 galaxies were originally observedoriginally observed

Purpose: measuring integrated light from galaxy nuclei Purpose: measuring integrated light from galaxy nuclei and constructing stellar population models of galaxies and constructing stellar population models of galaxies and globular clusters and globular clusters determining spectral types and determining spectral types and luminosities of a wide range of reddened starsluminosities of a wide range of reddened stars

These observations were not originally intended to be These observations were not originally intended to be the basis for a standard photometric system, but to the basis for a standard photometric system, but to supplement UBV-photometry by segregating stellar supplement UBV-photometry by segregating stellar temperature and luminosity effects from reddening and temperature and luminosity effects from reddening and ultraviolet excessultraviolet excess

The DDO photometric systemThe DDO photometric system 33

The DDO photometric The DDO photometric systemsystem

System specifications and standard stars were System specifications and standard stars were revised by McClure (1975) because:revised by McClure (1975) because:

– Many nights at Toronto were of dubious Many nights at Toronto were of dubious photometric quality (= large random errors), photometric quality (= large random errors),

– Bandpass of the ultaviolet interference filter Bandpass of the ultaviolet interference filter measuring line blanketing (38) was too narrow measuring line blanketing (38) was too narrow limiting magnitude for observations of late- limiting magnitude for observations of late-type stars was severely restricted type stars was severely restricted

– Only color indices were published (lack of a Only color indices were published (lack of a magnitude system difficults detection of magnitude system difficults detection of variable stars) variable stars)

– Original Toronto filter set deteriorated shortly Original Toronto filter set deteriorated shortly after observations were completedafter observations were completed

The DDO photometric systemThe DDO photometric system 44

The DDO photometric The DDO photometric systemsystem

New observations of 285 standard stars made on New observations of 285 standard stars made on the 41-cm and 91-cm reflecting telescopes at Kitt the 41-cm and 91-cm reflecting telescopes at Kitt Peak National Observatory (1971-1973) replaced Peak National Observatory (1971-1973) replaced the original ones for the calculationsthe original ones for the calculations

Equipment used: conventional single channel Equipment used: conventional single channel photometers with dry-ice-cooled 1P21 photometers with dry-ice-cooled 1P21 photomultipliersphotomultipliers

Magnitude system for the 48 filter was Magnitude system for the 48 filter was incorporated (48M = V + 0,375 (B-V) for A-K incorporated (48M = V + 0,375 (B-V) for A-K stars)stars)

The DDO photometric systemThe DDO photometric system 55

The DDO Filters The DDO Filters (acc. McClure (acc. McClure 1975)1975)

Specifications

The DDO photometric systemThe DDO photometric system 66

The DDO Filters The DDO Filters (acc. McClure (acc. McClure 1975)1975)

Transmission curves

The DDO photometric systemThe DDO photometric system 77

The DDO Filters The DDO Filters (acc. McClure (acc. McClure 1975)1975)

Transmissions of the standard DDO set

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The DDO Filters The DDO Filters (acc. McClure (acc. McClure 1975)1975)

The following four filters have been The following four filters have been used for Population I stars to used for Population I stars to provide measurementes of Tprovide measurementes of Teffeff, , surface gravity and abundance of surface gravity and abundance of heavy elements:heavy elements:

The 48 filter (λ4886):The 48 filter (λ4886):– Similar to the HSimilar to the Hββ filter of filter of

Crawford & Mander, but its use Crawford & Mander, but its use here is not connected with the here is not connected with the hydrogen linehydrogen line

– Situated in a region of absorption Situated in a region of absorption by MgH by MgH

The 45 filter bandpass (λ4517) :The 45 filter bandpass (λ4517) :– Situated in a region relatively Situated in a region relatively

free of strong spectral featuresfree of strong spectral features– Comparison bandpass for the 42 Comparison bandpass for the 42

and 48 filters and 48 filters

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The DDO Filters The DDO Filters (acc. McClure (acc. McClure 1975)1975)

The 42 filter bandpass (λ4257) The 42 filter bandpass (λ4257) ::– Located shortward of the Located shortward of the

main CH absorption of the main CH absorption of the G band (λ4299) and G band (λ4299) and longward of the violet longward of the violet cyanogen-band head cyanogen-band head (λ4216)(λ4216)

The 41 filter bandpass (λ4166) The 41 filter bandpass (λ4166) : : – Located in the region of the Located in the region of the

violet cyanogen-band violet cyanogen-band absorptionabsorption

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The DDO Filters The DDO Filters (acc. McClure (acc. McClure 1975)1975)

For very metal-poor Population II stars For very metal-poor Population II stars (weak or non-existent CN band) or (weak or non-existent CN band) or where more than the abundance of where more than the abundance of CNO elements is of interest, metallic-CNO elements is of interest, metallic-line blanketing index are necessary: line blanketing index are necessary:

The 38b filter (λ3815) :The 38b filter (λ3815) :– Located shortward of the break Located shortward of the break

near λ4000 (due to metallic near λ4000 (due to metallic blanketing in UV)blanketing in UV)

The 35 filter (λ3460) :The 35 filter (λ3460) :– Identical to the “u” filter of Identical to the “u” filter of

Crawford & Barnes (1970)Crawford & Barnes (1970)– Located shortward of the Balmer Located shortward of the Balmer

discontinuity and longward of the discontinuity and longward of the region where the Earth´s region where the Earth´s atmospheric absorption becomes atmospheric absorption becomes totaltotal

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The DDO Standard Stars The DDO Standard Stars (acc. (acc. McClure 1975)McClure 1975)

Almost all stars observed by McClure and van den Almost all stars observed by McClure and van den Bergh (1968) were retained (about 2/3). Bergh (1968) were retained (about 2/3).

They were originally chosen acc. to following criteria:They were originally chosen acc. to following criteria:– Stars as bright as possible (to provide an easily Stars as bright as possible (to provide an easily

observed set of standards)observed set of standards)– Spectral type range from O9 to M6, including all Spectral type range from O9 to M6, including all

luminosity classesluminosity classes– Both metal-poor and metal-rich starsBoth metal-poor and metal-rich stars– A number of unusual stars should be included A number of unusual stars should be included

(e.g. strong cyanogen absorption, peculiar, WR, (e.g. strong cyanogen absorption, peculiar, WR, metallic-lines, etc)metallic-lines, etc)

– Half were picked to be brighter than 6.0mag, and Half were picked to be brighter than 6.0mag, and half between 6.0 and 8.0 maghalf between 6.0 and 8.0 mag

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The DDO Standard Stars The DDO Standard Stars (acc. (acc. McClure 1975) McClure 1975)

IIt is always wise to limit the temperature range of standard t is always wise to limit the temperature range of standard stars observed. Most standards should be similar to the stars observed. Most standards should be similar to the

program stars in spectral type and luminosity classprogram stars in spectral type and luminosity class

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The DDO Standard Stars The DDO Standard Stars (acc. (acc. McClure 1975) McClure 1975)

IIt is always wise to limit the temperature range of standard t is always wise to limit the temperature range of standard stars observed. Most standards should be similar to the stars observed. Most standards should be similar to the

program stars in spectral type and luminosity classprogram stars in spectral type and luminosity class

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The DDO color indicesThe DDO color indices

Succesive color indices are formed from Succesive color indices are formed from measurements through each of the filter measurements through each of the filter bandpasses. bandpasses.

Example: for the intensity of light through Example: for the intensity of light through filters 45 and 48 filters 45 and 48 C(45-48) = 2,5 log C(45-48) = 2,5 log (I48/I45)(I48/I45)

The C(45-48) index:The C(45-48) index:– Sensitivity to surface gravity for late-type Sensitivity to surface gravity for late-type

stars (due to MgH absorption region for stars (due to MgH absorption region for filter 48)filter 48)

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The DDO color indicesThe DDO color indices The C(42-45) index: The C(42-45) index:

- Designed to measure the - Designed to measure the break in the continuum break in the continuum of late-type stars due to of late-type stars due to the G band of CH and the G band of CH and other nearby linesother nearby lines-The G band break is -The G band break is primarily sensitive to primarily sensitive to spectral type or Teffspectral type or Teff- Affected by - Affected by microturbulence (in the 42 microturbulence (in the 42 band CH lines presumably band CH lines presumably makes it more effective). makes it more effective). The effect is stronger in The effect is stronger in coolest models and coolest models and decreases with increasing decreases with increasing TeffTeff

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The DDO color indicesThe DDO color indices The C(41-42) index:The C(41-42) index:

– Also called “cyanogen-index”Also called “cyanogen-index”– Sensitivity to luminosity (Lindblad, 1922)Sensitivity to luminosity (Lindblad, 1922)– Sensitivity to abundance of heavy elements (C, N)Sensitivity to abundance of heavy elements (C, N)

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The DDO color indicesThe DDO color indices The C(38-42) index:The C(38-42) index:

– Defined as [C(38-42) = Defined as [C(38-42) = C(38-41)+C(41-42)]C(38-41)+C(41-42)]

– Designed to be a Designed to be a blanketing index blanketing index

The C(35-38) index:The C(35-38) index:– Measures the Balmer Measures the Balmer

discontinuitydiscontinuity– Sensitive to both Sensitive to both

temperature and luminositytemperature and luminosity– Index of limited use for late Index of limited use for late

stars (except for those too stars (except for those too hot for C(45-48))hot for C(45-48))

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The DDO color-color The DDO color-color diagramsdiagrams

The C(45-48) vs C(42-45) diagramm:The C(45-48) vs C(42-45) diagramm:– The most basic and important in the DDO system The most basic and important in the DDO system – It enables two-dimensional spectral classification as It enables two-dimensional spectral classification as

accurate as the MK-systemaccurate as the MK-system– Central role in the determination of absolute Central role in the determination of absolute

magnitudes and metallicities of late-type Pop I giants magnitudes and metallicities of late-type Pop I giants when combined with the C(41-42) cyanogen indexwhen combined with the C(41-42) cyanogen index

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The DDO color-color The DDO color-color diagramsdiagrams

The C(41-42) vs C(42-45) diagramm: The C(41-42) vs C(42-45) diagramm: Very sensitive to overall metallicity (insofar as C and N vary Very sensitive to overall metallicity (insofar as C and N vary in lockstep with Fe and the rest of the metals)in lockstep with Fe and the rest of the metals)

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The DDO color-color The DDO color-color diagramsdiagrams

The C(38-42) vs C(45-48) diagramm: The C(38-42) vs C(45-48) diagramm:

Allows luminosity classificationAllows luminosity classification

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Impact of molecular absorption Impact of molecular absorption on DDO photometryon DDO photometry

DDO photometry measures a relatively narrow spectral DDO photometry measures a relatively narrow spectral window. It includes a number of strong molecular window. It includes a number of strong molecular absorption features in late-type stars. It is interesting absorption features in late-type stars. It is interesting knowing the resulting color offsets relative to the knowing the resulting color offsets relative to the original model for each molecule MgH, SiH, CH, CNoriginal model for each molecule MgH, SiH, CH, CN

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ReferencesReferences McClure, Robert (1975), Standard Stars for DDO McClure, Robert (1975), Standard Stars for DDO

photometry, The Astronomical Journal, Vol 81, Nr. photometry, The Astronomical Journal, Vol 81, Nr. 3, p. 1033, p. 103

Tripicco, M.J. and Bell, R.A. (1991), Exploring the Tripicco, M.J. and Bell, R.A. (1991), Exploring the properties of the DDO system using synthetic properties of the DDO system using synthetic colors, The Astronomical Journal, Vol. 102, Nr. 2, colors, The Astronomical Journal, Vol. 102, Nr. 2, p. 744p. 744

McClure, R. and van den Bergh, S. (1968), Five-McClure, R. and van den Bergh, S. (1968), Five-Color Intermediate-Band Photometry of Stars, Color Intermediate-Band Photometry of Stars, Clusters and Galaxies, The Astronomical Journal, Clusters and Galaxies, The Astronomical Journal, Vol 73, Nr. 5, Part 1, p. 313 Vol 73, Nr. 5, Part 1, p. 313