Microlensing Towards the Galactic Bulge

Udalski, A.; Szymański, M. K.; Kałużny, J.; Kubiak, M.; Mateo, Mario; Preston, George W.; Krzemiński, W.; Paczyński, B.

doi:10.1007/978-94-011-0922-2_31

Cited by 714 publications

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“…In Tables 1 and 2 we show a compilation of some results. Gaia should be better than these (Udalski et al 1994(Udalski et al , 1995a(Udalski et al ,b, 1998 experiments because its precision is higher. Table 3 shows the results of the analysis of the Hipparcos results.…”

Section: Estimation Of the Number Of Variable Starsmentioning

confidence: 95%

First thoughts about variable star analysis

Eyer¹

1999

Open Astronomy

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Abstract.The Gaia mission characteristics permit to estimate its impact on the variable star research. During its five-year operation Gaia will produce about 100 photometric measurements in each passband of the Sloan system for about 1 billion stars. Thanks to our knowledge of the Hipparcos data and the similarities between these two missions, we can forecast that Gaia will detect tens of millions of new variable stars.Key words: stars: variables, photometry -orbiting observatories: Gaia INTRODUCTIONThe first step of variable star analysis is to study the time series of individual measurements per object for obtaining and to reduce them to mean magnitudes, light curves, intrinsic dispersions, noises, periods, epochs, light curves, etc. The ability to obtain this information depends on the signal parameters (amplitude, shape) and the measurement and reduction procedures in the satellite (time sampling, number of measurements, noise). The accurate estimation of the noise and the ability to identify outlying values are two crucial prerequisites for variable star analysis. Therefore, precise calibration procedures are needed, e.g. the control of star extraction in crowded fields, controlled ageing effects, etc. ESTIMATION OF THE NUMBER OF VARIABLE STARSWe binned the star population measured by Gaia, and applied the fraction of variable stars found in the Hipparcos analysis for the same population and the same magnitude precision. The model inputs are the following:• The errors of individual measurements. In our estimation we adopted their magnitude dependence from H0g et al. (1998) for the G magnitude and an error of 0.01 mag for V < 17). The saturation affects only a small number of bright stars and is not taken into account.• The star population.We have used the starcount model (iV(My), N(my) as a function of V-I) given by Torra et al. (1999). The total number of stars with V < 20 mag is 912 millions.• The variability detection threshold for the foreseen Gaia time sampling and noise distribution as a function of magnitude (established from Hipparcos results. With this model, we estimate 26 million variable stars, among them 7 million periodic variables.Some comments can be added: • The Gaia star sample will differ from the Hipparcos sample by the presence of more numerous red dwarf stars. Red dwarfs generally are variable with pseudo-periodic variations of several days (BY Draconis stars). A large fraction of them can be detected with Gaia.• Because the Hipparcos survey is magnitude limited, sample biases are present when estimating the fraction of variables (for example, in the cases of EB or EW eclipsing binaries).• The Gaia time sampling will be semi-regular and will introduce aliasing frequencies when doing period search. This sampling will lower the ability to detect certain periods. In the Hipparcos database, the performance of the period search algorithms usually dropped when periods were close to 15 days (cf. Eyer et al 1994).• GAIA will also produce time series for stars in the Magellanic Clouds and for...

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Section: Estimation Of the Number Of Variable Starsmentioning

confidence: 95%

First thoughts about variable star analysis

Eyer¹

1999

Open Astronomy

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“…WASP, Pollacco et al 2006; HATnet, Bakos et al 2004; ASAS, Pojmanski 1997; OGLE, Udalski et al 1992; KELT, Pepper et al 2007). These data can provide an excellent source of information on many thousands of variable stars.…”

Section: Introductionmentioning

confidence: 99%

HD 24355 observed by theKepler K2mission: a rapidly oscillating Ap star pulsating in a distorted quadrupole mode

Holdsworth

Kurtz

Smalley

et al. 2016

Mon. Not. R. Astron. Soc.

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We present an analysis of the first Kepler K2 mission observations of a rapidly oscillating Ap (roAp) star, HD 24355 (V = 9.65). The star was discovered in SuperWASP broadband photometry with a frequency of 224.31 d −1 (2596.18 µHz; P = 6.4 min) and an amplitude of 1.51 mmag, with later spectroscopic analysis of low-resolution spectra showing HD 24355 to be an A5 Vp SrEu star. The high precision K2 data allow us to identify 13 rotationally split sidelobes to the main pulsation frequency of HD 24355. This number of sidelobes combined with an unusual rotational phase variation show this star to be the most distorted quadrupole roAp pulsator yet observed. In modelling this star, we are able to reproduce well the amplitude modulation of the pulsation, and find a close match to the unusual phase variations. We show this star to have a pulsation frequency higher than the critical cut-off frequency. This is currently the only roAp star observed with the Kepler spacecraft in Short Cadence mode that has a photometric amplitude detectable from the ground, thus allowing comparison between the mmag amplitude ground-based targets and the µmag spaced-based discoveries. No further pulsation modes are identified in the K2 data, showing this star to be a single-mode pulsator.

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“…Most of the OGLE-IV (phase 4) observations were taken in the Cousins I band, with occasional observations in Johnson V band (Udalski et al 2015). In the year 2014, OGLE Early Warning System (EWS) (Udalski et al 1994) detected 2049 microlensing candidates, of which event OGLE-2014-BLG-1760 was the 1760th one.…”

Section: Observationsmentioning

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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Microlensing Towards the Galactic Bulge

Cited by 714 publications

References 0 publications

First thoughts about variable star analysis

First thoughts about variable star analysis

HD 24355 observed by theKepler K2mission: a rapidly oscillating Ap star pulsating in a distorted quadrupole mode

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

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