The Luminosity Function and Initial Mass Function in the Galactic Bulge

Holtzman, Jon A.; Watson, A. M.; Baum, W. A.; Grillmair, Carl J.; Groth, Edward J.; Light, R. M.; Lynds, Roger; O'Neil, Earl J.

doi:10.1086/300336

Cited by 214 publications

(284 citation statements)

References 30 publications

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“…There is an additional enhancement factor due to the fact that the foreground disk stars are intrinsically fainter and that the stellar luminosity function rises for fainter stars, but the difference between the disk stars at 5 kpc and the bulge stars at 8 kpc is only 1 mag. From Holtzman et al (1998) we see that this factor is at most %10 if we select a source magnitude such that it is 1-2 mag above the bulge main-sequence turnoff. For magnitudes that correspond to bulge main-sequence stars, it is less than a factor of 2.…”

Section: Microlensing Parallax Selection Effectsmentioning

confidence: 98%

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Bennett

Becker

Quinn

et al. 2002

ApJ

137

134

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We present an analysis of the longest timescale microlensing events discovered by the MACHO Collaboration during a 7 year survey of the Galactic bulge. We find six events that exhibit very strong microlensing parallax signals due, in part, to accurate photometric data from the GMAN and MPS collaborations. The microlensing parallax fit parameters are used in a likelihood analysis, which is able to estimate the distances and masses of the lens objects based on a standard model of the Galactic velocity distribution. This analysis indicates that the most likely masses of five of the six lenses are greater than 1 M , which suggests that a substantial fraction of the Galactic lenses may be massive stellar remnants. This could explain the observed excess of long-timescale microlensing events. The lenses for events MACHO-96-BLG-5 and MACHO-98-BLG-6 are the most massive, with mass estimates of M=M ¼ 6 þ10 À3 and M=M ¼ 6 þ7 À3 , respectively. The observed upper limits on the absolute brightness of main-sequence stars for these lenses are less than 1 L , so both lenses are black hole candidates. The black hole interpretation is also favored by a likelihood analysis with a Bayesian prior using a conventional model for the lens mass function. We consider the possibility that the source stars for some of these six events may lie in the foreground Galactic disk or in the Sagittarius (Sgr) dwarf galaxy behind the bulge, but we find that bulge sources are likely to dominate our microlensing parallax event sample. Future Hubble Space Telescope observations of these events can either confirm the black hole lens hypothesis or detect the lens stars and provide a direct measurement of their masses. Future observations of similar events by the Space Interferometry Mission or the Keck or VLT interferometers, as explained by Delplancke, Gó rski, & Richichi, will allow direct measurements of the lens masses for stellar remnant lenses as well.

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Section: Microlensing Parallax Selection Effectsmentioning

confidence: 98%

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Bennett

Becker

Quinn

et al. 2002

ApJ

137

134

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“…Simple exponential models for the disk, for example, predict that in Baade's window at least half of the stars visible are actually disk stars, and not bulge stars. Employing photometry alone, it is not possible to effectively sort the populations; bulge and disk populations overlap in color, especially near the turnoff (Holtzman et al 1998), greatly complicating the use of color-magnitude diagrams derived from the Hubble Space Telescope (HST) for age determination. Blue stragglers extending brighter than the turnoff in an old population overlap with the main-sequence locus of a young population.…”

Section: Introductionmentioning

confidence: 99%

[ITAL]Hubble Space Telescope[/ITAL] WFPC2 Proper Motions in Two Bulge Fields: Kinematics and Stellar Population of the Galactic Bulge

Kuijken

Rich²

2002

The Astronomical Journal

148

209

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We report proper-motion dispersions for stars in the direction of two fields of the Galactic bulge, using Hubble Space Telescope Wide Field Planetary Camera 2 images taken 6 years apart. Our two fields are Baade's window [(l, b) = (1=13, À3=77)] and Sgr I [(l, b) = (1=25, À2=65)]. Our proper-motion dispersions are in good agreement with prior ground-and space-based proper-motion studies in bulge fields, but in contrast to some prior studies, we do not exclude any subset of stars from our sample. In Baade's window, we find the l and b proper-motion dispersions are 2.9 and 2.5 mas yr À1 , while in Sgr I, they are 3.3 and 2.7 mas yr À1 , respectively. For the first time, we can clearly separate the foreground disk stars out from the bulge because of their large mean apparent proper motion. The population with nondisk kinematics (which we conclude to be the bulge) has an old main-sequence turnoff point, similar to those found in old, metal-rich bulge globular clusters, while those stars selected to have disk kinematics lie on a fully populated main sequence. Separating main-sequence stars by luminosity, we find strong evidence that the bulge population is rotating, largely explaining observations of proper-motion anisotropy in bulge fields. Because we have isolated such a pure sample of stars in the bulge, we have one of the clearest demonstrations that the old stellar population of the inner bulge/bar is in fact rotating.

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“…Such stars would have a much larger microlensing event rate, so they could be preferentially lensed by bulge stars. It is also possible that the CMD in this field may be noticeably different than that of Baade's window where the Holtzman et al (1998) image was taken.…”

Section: Calibration and Source Propertiesmentioning

confidence: 99%

“…We take this average as the correct color of the source. The green points in the color−magnitude diagram (CMD) depicted by Figure 4 show the Hubble Space Telescope (HST) CMD plot (Holtzman et al 1998) shifted to have the same red clump centroid position as the OGLE-III stars within 140″ of the source star, and the cyan point shows the color of the source. The source color is slightly bluer than the main-sequence-star distribution, shown with green points in the HST CMD in Figure 4.…”

Section: Calibration and Source Propertiesmentioning

confidence: 99%

Discovery of a Gas Giant Planet in Microlensing Event Ogle-2014-BLG-1760

Bhattacharya

Bennett

Bond

et al. 2016

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We present the analysis of the planetary microlensing event OGLE-2014-BLG-1760, which shows a strong lightcurve signal due to the presence of a Jupiter mass ratio planet. One unusual feature of this event is that the source star is quite blue, with -=  V I 1.48 0.08. This is marginally consistent with a source star in the Galactic bulge, but it could possibly indicate a young source star on the far side of the disk. Assuming a bulge source, we perform a Bayesian analysis assuming a standard Galactic model, and this indicates that the planetary system resides in or near the Galactic bulge at =  D 6.9 1.1 kpc , and a projected star-planet separation of = -+ a 1.75 0.33 0.34 au. The lens-source relative proper motion is m =  6.5 1.1 rel mas yr −1 . The lens (and stellar host star) is estimated to be very faint compared to the source star, so it is most likely that it can be detected only when the lens and source stars start to separate. Due to the relatively high relative proper motion, the lens and source will be resolved to about ∼46 mas in 6-8 yr after the peak magnification. So, by 2020-2022, we can hope to detect the lens star with deep, high-resolution images.

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The Luminosity Function and Initial Mass Function in the Galactic Bulge

Cited by 214 publications

References 30 publications

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

Gravitational Microlensing Events Due to Stellar‐Mass Black Holes

[ITAL]Hubble Space Telescope[/ITAL] WFPC2 Proper Motions in Two Bulge Fields: Kinematics and Stellar Population of the Galactic Bulge

Discovery of a Gas Giant Planet in Microlensing Event Ogle-2014-BLG-1760

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