The Photometric The Photometric Properties ofProperties of

NGC 6134 and Hogg 19NGC 6134 and Hogg 19

SDSS SDSS u’g’r’i’z’ u’g’r’i’z’ Open Cluster Survey:Open Cluster Survey:

Credit: http://www.sdss.org Credit: SMARTS consortium

The Sloan Digital Sky SurveyThe Sloan Digital Sky Survey

Main goals of SDSS:Main goals of SDSS: Mapping of large-scale structure Mapping of large-scale structure

(galaxies and quasars)(galaxies and quasars) Accurate redshifts using Accurate redshifts using

spectroscopy (10spectroscopy (1066 galaxies, 10 galaxies, 1055 quasars)quasars)

SDSS looks back in time as it SDSS looks back in time as it looks farther out in spacelooks farther out in space

SDSS aims to obtain high-resolution imaging of ¼ SDSS aims to obtain high-resolution imaging of ¼ of the entire sky in five different colors (of the entire sky in five different colors (ugriz ugriz filter filter set)set)

Wedge diagram of galaxy distributions (Doroshkevich et al. 2004)

z=6.4 quasar: 13 billion lyr

(universe ~800 million years old)Credit: SDSS at Apache Point

Spiral galaxy NGC 6070

Credit: SDSS collaboration

Open ClustersOpen Clusters

Approximately 105 open clusters and 10 “low-density” globular Approximately 105 open clusters and 10 “low-density” globular clusters observed with clusters observed with u’g’r’i’z’u’g’r’i’z’

Clusters span a range of ages and metallicitiesClusters span a range of ages and metallicities Can be used to “back-calibrate” SDSS, and verify Girardi et al. Can be used to “back-calibrate” SDSS, and verify Girardi et al.

(2004) isochrones(2004) isochrones Open clusters are interesting for stellar astrophysics because Open clusters are interesting for stellar astrophysics because

the stars in the cluster have roughly the same:the stars in the cluster have roughly the same: DistanceDistance AgeAge Chemical compositionChemical composition

But there are a variety of masses in the cluster, allowing for a But there are a variety of masses in the cluster, allowing for a sample of different stars for studies of stellar evolutionsample of different stars for studies of stellar evolution

M6M23

M67

Credit: http://www.seds.org

H-R DiagramsH-R Diagrams There is a relationship between a star’s “absolute” There is a relationship between a star’s “absolute”

luminosity and it’s temperature (or color)luminosity and it’s temperature (or color)

Most stars fall along Most stars fall along the Main Sequence the Main Sequence (the hydrogen burning (the hydrogen burning phase of their life phase of their life cycle)cycle)

After burning their After burning their hydrogen, stars move hydrogen, stars move off the main sequence off the main sequence to the Red Giant to the Red Giant branch branch

Credit: http://www.smv.org/jims/l6.htm

H-R Diagrams and Stellar EvolutionH-R Diagrams and Stellar Evolution

Magnitudes and ColorsMagnitudes and Colors

Astronomers use a logarithmic scale to represent the luminosity of Astronomers use a logarithmic scale to represent the luminosity of stars:stars:

where fwhere fvv is the flux per unit frequency incident on the atmosphere and S is the flux per unit frequency incident on the atmosphere and Svv is the system is the system quantum efficiencyquantum efficiency

The brighter the object, the smaller the magnitude!The brighter the object, the smaller the magnitude!

The color of an object can be represented by the difference in its The color of an object can be represented by the difference in its magnitude between two filtersmagnitude between two filters e.g. (e.g. (u’ – g’ u’ – g’ ), (), (g’ – r’ g’ – r’ ), (), (r’ – i’ r’ – i’ ), and (), and (i’ – z’ i’ – z’ ))

For black bodies, color is related to temperature by Wien’s Law: For black bodies, color is related to temperature by Wien’s Law:

60.48)(log

)(loglog5.2

Sd

SfdmAB

T

Kcm

2897.0max

Theoretical IsochronesTheoretical Isochrones Stars in open clusters are at approx. the same Stars in open clusters are at approx. the same

distancedistance The proportionality between “observed” and “absolute” The proportionality between “observed” and “absolute”

luminosity for the stars is the sameluminosity for the stars is the same

The stars in the cluster should lie along an The stars in the cluster should lie along an “isochrone” dependent on age and metallicity“isochrone” dependent on age and metallicity

For NGC 6134 and Hogg 19 we used the Girardi et For NGC 6134 and Hogg 19 we used the Girardi et al. (2004) isochrones for the al. (2004) isochrones for the u’g’r’i’z’ u’g’r’i’z’ systemsystem

Example of Girardi et al. (2004) color-magnitude diagrams for a cluster of solar metallicity with increasing age (107,108,109,1010 years)

Data ReductionData Reduction We have “raw” images from two telescopes from which we need We have “raw” images from two telescopes from which we need

to extract the actual photons hitting the detector (and infer the to extract the actual photons hitting the detector (and infer the photons actually leaving the star)photons actually leaving the star) The images of Hogg 19 and NGC 6134 were reduced with The images of Hogg 19 and NGC 6134 were reduced with

version 8.1 of the SDSS pipeline (version 8.1 of the SDSS pipeline (mtFrames, excal,mtFrames, excal, and and kalikali)) mtFramesmtFrames performs flat-fielding, bias subtraction, and aperture performs flat-fielding, bias subtraction, and aperture

photometryphotometry excal excal finds photometric zeropoints using standard star fieldsfinds photometric zeropoints using standard star fields kali kali applies the fitted photometric data to the lists of applies the fitted photometric data to the lists of

aperture photometryaperture photometry

Isochrone FitsIsochrone Fits After reducing the images with After reducing the images with

mtpipe, mtpipe, we had a list of aperture we had a list of aperture photometry from both the CTIO 0.9 photometry from both the CTIO 0.9 m and CTIO Curtis-Schmidt m and CTIO Curtis-Schmidt telescopestelescopes

The lists were combined – if an The lists were combined – if an object was in both lists, the object was in both lists, the observed magnitude with the observed magnitude with the smallest photon noise was usedsmallest photon noise was used

We matched our data with existing We matched our data with existing data in the WEBDA open cluster data in the WEBDA open cluster database and plotted the isochrones database and plotted the isochrones over top our dereddened data over top our dereddened data For NGC 6134, proper motion studies For NGC 6134, proper motion studies

were available to assign a cluster were available to assign a cluster membership probabilitymembership probability

Coordinates of Red Giants, Coordinates of Red Giants, Spectroscopic Binaries, and cluster Spectroscopic Binaries, and cluster stars were also availablestars were also available

No data were available for Hogg 19No data were available for Hogg 19

CTIO 0.9 m

CTIO Curtis-Schmidt

NGC 6134NGC 6134 NGC 6134 is an intermediate age, moderately NGC 6134 is an intermediate age, moderately

concentrated open cluster concentrated open cluster Several past studies have determined distance, age, and Several past studies have determined distance, age, and

metallicity by fitting theoretical isochronesmetallicity by fitting theoretical isochrones We used We used u’g’r’i’z’u’g’r’i’z’ filters and Girardi et al. (2004) filters and Girardi et al. (2004)

isochronesisochrones

NGC 6134: ResultsNGC 6134: Results

We find:We find:

Distance = 800Distance = 800±100 ±100 pcpc

Age = 1.0 Age = 1.0 ±0.2 Gyr±0.2 Gyr

[Z/Z[Z/Z] = 0.0 ±0.1] = 0.0 ±0.1

Our results are in Our results are in agreement with previous agreement with previous studies, although we find studies, although we find a lower metallicity than a lower metallicity than the recent study by the recent study by Bruntt et al. (1999)Bruntt et al. (1999)

Hogg 19Hogg 19

Hogg 19 is a sparse open cluster which adjoins NGC Hogg 19 is a sparse open cluster which adjoins NGC 6134, first discovered by A. R. Hogg (1965) 6134, first discovered by A. R. Hogg (1965)

If Hogg 19 exists, If Hogg 19 exists, it is barely it is barely discernable from discernable from the background the background stars stars

Contamination Contamination from the field from the field stars reduces the stars reduces the precision with precision with which the which the isochrones can isochrones can be fit to the be fit to the cluster starscluster stars

34’

Does Hogg 19 exist?Does Hogg 19 exist?

NGC 6134

Hogg 19

* Background

Does Hogg 19 exist?Does Hogg 19 exist?Hogg 19 background

1

background2

background3

Hogg 19: ResultsHogg 19: Results

We find the data are We find the data are consistent with:consistent with:

Distance = 550Distance = 550±100 ±100 pcpc

Age = 3.75 Age = 3.75 ±1.25 Gyr±1.25 Gyr

[Z/Z[Z/Z] = -0.8 ±0.4] = -0.8 ±0.4

We were unable to We were unable to make a robust make a robust determination of age or determination of age or metallicity, although it metallicity, although it appears to be quite old appears to be quite old and metal poorand metal poor

Summary and Future WorkSummary and Future Work We analyzed the We analyzed the u’g’r’i’z’u’g’r’i’z’ photometry of NGC 6134 and Hogg 19 photometry of NGC 6134 and Hogg 19

and plotted C-M and C-C diagramsand plotted C-M and C-C diagrams

For NGC 6134, we were able to determine values for distance For NGC 6134, we were able to determine values for distance (~800 pc), age (~1.0 Gyr), and metallicity ([Z/Z(~800 pc), age (~1.0 Gyr), and metallicity ([Z/Z] ] ≈ 0.0)≈ 0.0)

Our data indicate that Hogg 19 exists (due to presence of several Our data indicate that Hogg 19 exists (due to presence of several red giants in the Hogg field)red giants in the Hogg field)

We find the data consistent with a distance of ~550 pc for Hogg We find the data consistent with a distance of ~550 pc for Hogg 19, but cannot make a robust determination of age or metallicity19, but cannot make a robust determination of age or metallicity

Spectroscopy may be taken on Hogg 19 to better determine Spectroscopy may be taken on Hogg 19 to better determine cluster membership (or existence)cluster membership (or existence)

Future studies will be conducted on the remaining clusters in the Future studies will be conducted on the remaining clusters in the survey – the immediate goal is to publish a sample of open survey – the immediate goal is to publish a sample of open clusters covering a range of ages and metallicitiesclusters covering a range of ages and metallicities

Repeat observations may be pursued to hunt for variables stars Repeat observations may be pursued to hunt for variables stars (to improve distance estimates)(to improve distance estimates)

AcknowledgementsAcknowledgements

I appreciate the help of everyone who made this I appreciate the help of everyone who made this project possible:project possible: Douglas TuckerDouglas Tucker Allyn SmithAllyn Smith Roger Dixon, Erik Ramberg, and Maxine HronekRoger Dixon, Erik Ramberg, and Maxine Hronek The internsThe interns