Stellar Proper Motions in the Galactic Bulge from Deep Hubble Space Telescope ACS WFC Photometry

By W. Clarkson, K. Sahu, Jay Anderson, T. Smith, T. Brown, R. Rich, S. Casertano, H. Bond, M. Livio, D. Minniti and 4 more. 2008

143 citations recorded by the source corpus.

We present stellar proper motions in the Galactic bulge from the Sagittarius Window Eclipsing Extrasolar Search (SWEEPS) project using ACS WFC on HST. Proper motions are extracted for more than 180,000 objects, with >81,000 measured to accuracy better than 0.3 mas yr−1 in both coordinates. We report several results based on these measurements: (1) Kinematic separation of bulge from disk allows a sample of >15,000 bulge objects to be extracted based on ≥6 σ detections of proper motion, with <0.2% contamination from the disk. This includes the first detection of a candidate bulge blue straggler population. (2) Armed with a photometric distance modulus on a star-by-star basis, and using the large number of stars with high-quality proper-motion measurements to overcome intrinsic scatter, we dissect the kinematic properties of the bulge as a function of distance along the line of sight. This allows us to extract the stellar circular speed curve from proper motions alone, which we compare with the circular speed curve obtained from radial velocities. (3) We trace the variation of the {l, b} velocity ellipse as a function of depth. (4) Finally, we use the density-weighted {l, b} proper-motion ellipse produced from the tracer stars to assess the kinematic membership of the 16 transiting planet candidates discovered in the Sagittarius Window; the kinematic distribution of the planet candidates is consistent with that of the disk and bulge stellar populations.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/77a5dc12f0cf2df798b8d00ec72bebf42182f1f4

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In Astronomy and Astrophysics

1. O. Gerhard
2. C. Wegg
3. C. Conroy
4. L. Hernquist
5. P. Hopkins
6. A. Renzini
7. M. Zoccali
8. Christopher J. Conselice

In Instrumentation

1. O. Gerhard
2. C. Wegg
3. M. Zoccali
4. C. Conroy
5. A. Renzini
6. A. McWilliam
7. M. Schultheis
8. V. Hill

Citations in the corpus

• OUR MILKY WAY AS A PURE-DISK GALAXY—A CHALLENGE FOR GALAXY FORMATION (2010, background): “The bulge of our Galaxy is>99% made of stars that are at least 5 Gyr old (Clarkson et al. 2008) with a wide range of metal abundances (McWilliam & Rich 1994; Fulbright et al. 2006; Zoccali et al. 2008).”
• Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants (2011, background): “…published by EDP Sciences A54, page 1 of 12 [Fe/H] = −1.5 to [Fe/H] = 0.5, with a peak at solar metallicity (e.g. Zoccali et al. 2003, 2008; Clarkson et al. 2008; Brown et al. 2010, and references therein) and that the formation of the bulge was fast as evidenced by the enhanced alpha…”
• Reddening and metallicity maps of the Milky Way bulge from VVV and 2MASS II. The complete high resolution extinction map and implications for Galactic bulge studies (2012, background): “…by analyzing the stellar ages and chemical abundances (McWilliam & Rich 1994; Zoccali et al. 2003; Fulbright et al. 2007; Rich et al. 2007; Lecureur et al. 2007; Zoccali et al. 2008; Clarkson et al. 2008; Brown et al. 2010; Bensby et al. 2010, 2011; Johnson et al. 2011; Gonzalez et al. 2011b).”
• TWO RED CLUMPS AND THE X-SHAPED MILKY WAY BULGE (2010, methodology): “Extant age studies by Zoccali et al. (2003) and Clarkson et al. (2008) should be supplemented with a photometric survey for the ages of bulge stars at (l, b)=(±5,−8), in order to completely rule-out the possibility that age is responsible for the luminosity difference between the two RCs at this…”
• VISTA Variables in the Via Lactea (VVV): The public ESO near-IR variability survey of the Milky Way (2009, background): “This is beyond the minimum value to distinguish bulge and disk populations, since the proper motion difference between them is∼ 6 miliarcs yr−1 in the galactic center region (Clarkson et al., 2008).”
• Dynamical modelling of the galactic bulge and bar: the Milky Way's pattern speed, stellar and dark matter mass distribution (2016, background): “…the bulge is still under debate with pieces of contradictory evidence: photometric studies of the color-magnitude diagram (CMD; Zoccali et al. 2003; Clarkson et al. 2008; Calamida et al. 2015) find that the bulge is older MNRAS 000, 1–25 (2016) than 10Gyr while spectroscopic age measurements of…”
• Predictions of the WFIRST Microlensing Survey. I. Bound Planet Detection Rates (2018, methodology): “We compared the predicted BGM1106 proper motions to Hubble Space Telescope (HST) proper motion measurements in the ∼11 arcmin2 SWEEPS field (Clarkson et al. 2008).”
• Vvv dr1: the first data release of the milky way bulge and southern plane from the near-infrared eso public survey vista variables in the via lactea (2011, background): “Although the distributions are wider than those presented in the HST analysis of Clarkson et al. (2008), the mean differences between proper motions of disk and bulge are still evident based on these data showing differences of (∆µl,∆µb) = (3.39± 0.25, 1.25± 0.24) mas yr−1, in good agreement with…”
• THE HUBBLE SPACE TELESCOPE WIDE FIELD CAMERA 3 EARLY RELEASE SCIENCE DATA: PANCHROMATIC FAINT OBJECT COUNTS FOR 0.2–2 μm WAVELENGTH (2010, background): “Clarkson et al. (2008) show 17 similar proper motion values at R∼5 kpc, but in Baade’s window from multi-epoch HST/ACS images that are effectively complete to about I<∼ 21 mag given the more crowded images at low Galactic latitudes.”
• The metallicity distribution of bulge clump giants in Baade’s window (2011, background): “However, the main-sequence counterpart of this younger population has so far eluded deep colour–magnitude diagrams of low-reddening regions (Clarkson et al. 2008).”
• Insights on the Milky Way bulge formation from the correlations between kinematics and metallicity (2010, background): “…the age, colour−magnitude diagrams show that most of the Galactic bulge stars are older than 10 Gyr (Ortolani et al. 1995; Feltzing & Gilmore 2000; Zoccali et al. 2003; Clarkson et al. 2008) although an intermediate-age population exists (van Loon et al. 2003; Groenewegen & Blommaert 2005).”