Galactic structure studies with BATC star counts

Abstract. Red horizontal-branch (RHB) stars have been selected from the H catalogue to investigate their kinematics and spatial distribution. H parallaxes, literature radial velocities and H proper motions, together with models for the gravitational potential of the Milky Way allow a calculation of the actual velocity vectors and the orbits of the RHB stars. The velocity characteristics are used to define a halo population sample (HPS) in the collection of RHBs. The orbits lead statistically to an overall z-distance probability distribution, showing that the RHBs exhibit two populations, a disk one having a scale height of h disk 0.6 kpc and a halo one of 4 kpc. We have investigated the influence on our results of parallax accuracy and of a demarcation line in the HRD between the RHB and the red-giant (RG) star region. Neither of them show marked effects. We have performed the orbit analysis using the potential model of Allen & Santillan as well as of Dehnen & Binney. The results differ only slightly for the disk population, showing that these potential models are not a critical part of such orbit investigations. RHB scale height values are smaller than those found earlier for sdB stars, most likely because the samples of stars used had different spatial distributions a priori. The data do not allow us to specify a trend in the kinematic behaviour of star types along the horizontal branch.

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“…Recently, Chen et al (2001) found 330 ± 3 pc, while Du et al (2003) found 320 ± 15 pc. Our value of 120 pc is much smaller than those.…”

Section: General Comparisonmentioning

confidence: 99%

Kinematics of RHB stars to trace the structure of the Galaxy

Kaempf¹,

Boer²,

Altmann

2005

A&A

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“…We used the classical χ 2 statistic to estimate galactic model parameters, which is the most commonly method in recent studies (Phleps et al 2000(Phleps et al , 2005Chen et al 2001;Siegel et al 2002;Du et al 2003Du et al , 2006Jurić et al 2008;Bilir et al 2008a). The comparison of the logarithmic density functions derived from the observations and the analytical density laws is given in Fig.…”

Section: Estimation Of the Galactic Model Parametersmentioning

confidence: 99%

Estimation of galactic model parameters and metalicity distribution in intermediate latitudes with SDSS

Yaz

Karaali

2010

New Astronomy

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We estimated the galactic model parameters for a set of 20 intermediate-latitude fields with galactic longitudes 0 • ≤ l ≤ 100 • and 160 • ≤ l ≤ 240 • , included in the currently available Data Release 6 (DR6) of the Sloan Digital Sky Survey (SDSS), to explore their possible variation with galactic longitude. The local space densities of the thick disc and halo are almost the same for all fields, (n 2 /n 1 ) = 6.52% and (n 3 /n 1 ) = 0.35%, respectively, a result different than the one cited for highlatitude fields. The thin disc's scaleheight is 325 pc in the galactic centre changes to 369 pc in the third quadrant, which confirms the existence of disc flare, whereas the thick disc scaleheight is as large as 952 pc at galactic longitude l = 20 • and 10% lower at l = 160 • , which confirms the existence of the disc long bar in the direction l ≃ 27 • . Finally, the variation of the axis ratio of the halo with galactic longitude is almost flat, (c/a) = 0.56, except a slight minimum and a small maximum in the second and third quadrants, respectively, indicating an effect of the long bar which seems plausible for a shallow halo. We estimated the metallicities of unevolved G-type stars and discussed the metallicity gradient for different vertical distances. The metallicity gradient is d[M/H]/dz ∼ −0.30 dex kpc −1 for short distances, confirming the formation of this region of the Galaxy by dissipational collapse. However, its change is steeper in the transition regions of different galactic components. The metallicity gradient is almost zero for inner halo (5 < z < 10 kpc), indicating a formation of merger or accretion of numerous fragments such as dwarf galaxies.98.35.Ln Stellar content and populations; morphology and overall structure, 98.35.Gi Galactic halo

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“…We used the classical χ 2 method for the estimation of the Galactic model parameters, a method which is made in the studies of the Galactic structure that has been used in the determination of the most recent numerical values for the Galactic model parameters (Phleps et al 2000(Phleps et al , 2005Chen et al 2001;Siegel et al 2002;Du et al 2003Du et al , 2006Jurić et al 2008). The comparison of the logarithmic density functions derived from the observations and the analytical density laws are given in Figure 7, for four fields with Galactic longitudes l = 0, 90, 180 and 270 • .…”

Section: Estimation Of the Galactic Model Parametersmentioning

confidence: 99%

Estimation of Galactic Model Parameters in High Latitudes with SDSS

Bilir

Cabrera-Lavers

Karaali

et al. 2008

Publ. – Astron. Soc. Aust

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Abstract:We estimated the Galactic model parameters for a set of 36 high-latitude fields included in the currently available Data Release 5 (DR 5) of the Sloan Digital Sky Survey (SDSS), to explore their possible variation with the Galactic longitude. The thick disc scaleheight moves from ∼550 pc at 120 < l < 150 • to ∼720 pc at 250 < l < 290 • , while the thin disc scaleheight is as large as ∼195 pc in the anticenter direction and ∼15% lower at |l| < 30 • . Finally, the axis ratio (c/a) of the halo changes from a mean value of ∼0.55 in the two first quadrants of the Galaxy to ∼0.70 at 190 < l < 300 • . For the halo, the reason for the dependence of the model parameters on the Galactic longitude arises from the well known asymmetric structure of this component. However, the variation of the model parameters of the thin and thick discs with Galactic longitude originates from the gravitational effect of the Galactic long bar. Moreover, the excess of stars in quadrant I (quadrant III) over quadrant IV (quadrant II) is in agreement with this scenario.

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Galactic structure studies with BATC star counts

Cited by 44 publications

References 69 publications

Kinematics of RHB stars to trace the structure of the Galaxy

Kinematics of RHB stars to trace the structure of the Galaxy

Estimation of galactic model parameters and metalicity distribution in intermediate latitudes with SDSS

Estimation of Galactic Model Parameters in High Latitudes with SDSS

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