J/ApJ/874/30 RRab stars toward Baade's window with Blanco/DECam (Saha+, 2019) ================================================================================ Mapping the interstellar reddening and extinction toward Baade's window using minimum light colors of ab-type RR Lyrae stars: revelations from the de-reddened color-magnitude diagrams. Saha A., Vivas A.K., Olszewski E.W., Smith V., Olsen K., Blum R., Valdes F., Claver J., Calamida A., Walker A.R., Matheson T., Narayan G., Soraisam M., Cunha K., Axelrod T., Bloom J.S., Cenko S.B., Frye B., Juric M., Kaleida C., Kunder A., Miller A., Nidever D., Ridgway S. =2019ApJ...874...30S ================================================================================ ADC_Keywords: Stars, variable; Galactic plane; Photometry, ugriz Keywords: Galaxy: bulge ; Galaxy: stellar content ; Galaxy: structure ; ISM: dust, extinction ; methods: data analysis ; stars: variables: RR Lyrae Abstract: We have obtained repeated images of six fields toward the Galactic bulge in five passbands (u, g, r, i, z) with the DECam imager on the Blanco 4m telescope at CTIO. From more than 1.6 billion individual photometric measurements in the field centered on Baade's window, we have detected 4877 putative variable stars. A total of 474 of these have been confirmed as fundamental mode RR Lyrae stars, whose colors at minimum light yield line-of-sight reddening determinations, as well as a reddenning law toward the Galactic Bulge, which differs significantly from the standard R_V_=3.1 formulation. Assuming that the stellar mix is invariant over the 3 square-degree field, we are able to derive a line-of-sight reddening map with sub-arcminute resolution, enabling us to obtain de-reddened and extinction corrected color-magnitude diagrams (CMDs) of this bulge field using up to 2.5 million well-measured stars. The corrected CMDs show unprecedented detail and expose sparsely populated sequences: for example, delineation of the very wide red giant branch, structure within the red giant clump, the full extent of the horizontal branch, and a surprising bright feature that is likely due to stars with ages younger than 1Gyr. We use the RR Lyrae stars to trace the spatial structure of the ancient stars and find an exponential decline in density with Galactocentric distance. We discuss ways in which our data products can be used to explore the age and metallicity properties of the bulge, and how our larger list of all variables is useful for learning to interpret future LSST alerts. Description: We obtained images of six select fields toward the general direction of the Galactic center with the DECam imager on the Blanco 4m telescope at the Cerro-Tololo Inter-American Observatory (CTIO) over multiple epochs in five different passbands (u, g, r, i, z). B1 field (GLON:1.02,GLAT:-3.92) is centered on the well-known "Baade's Window" and gets close to the direction of the Galactic center while remaining relatively transparent. The journal of observations is given in Table 2; observations span 2013 May to 2015 April with exposure times of typically 300s in u and 100s in g, r, i, z. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file table2.dat 26 400 Journal of observations for field B1 in all bands table3.dat 35 120230 Photometry of ab-type RR Lyrae stars in field B1 table4.dat 178 474 RRab stars and their fitted parameters table5.dat 140 2553120 Positions and photometry of all stars used in the Color-Magnitude Diagrams -------------------------------------------------------------------------------- See also: V/141 : Light-Motion Curve Catalogue (LMCC) in Stripe 82 (Bramich+ 2008) J/AJ/114/2596 : RR Lyrae in new galactic bulge window (Blanco+, 1997) J/ApJ/597/323 : Cool stars at the Galactic Center (Blum+, 2003) J/ApJ/632/266 : WFPC2 photometry of the globular cluster M5 (Layden+, 2005) J/ApJ/708/717 : Light curve templates of RR Lyrae stars (Sesar+, 2010) J/AJ/142/187 : HST obs. of 7 Pop.II variable stars (Benedict+, 2011) J/ApJ/790/164 : Candidate bulge WDs in the SWEEPS field (Calamida+, 2014) J/ApJS/215/19 : APOKASC catalog of Kepler red giants (Pinsonneault+, 2014) J/AcA/64/177 : VI LCs of Galactic Bulge RR Lyrae (Soszynski+, 2014) J/A+A/573/A103 : Light curves for variables in 5 clusters (Skottfelt+, 2015) J/A+A/590/A9 : RGB stars in Galactic GC stellar parameters (Dias+, 2016) J/AJ/151/144 : ASPCAP weights for APOGEE chemical elements (Garcia+, 2016) J/MNRAS/456/3655 : Masses and ages of red giants (Martig+, 2016) J/AJ/153/179 : VVV Survey RR Lyr stars in South Gal. plane (Minniti+, 2017) J/AJ/154/231 : Multi-epoch multi-band photometry of B1-392 (Saha+, 2017) J/AJ/154/85 : CTIO/DECam photometry of RR Lyrae stars in M5 (Vivas+, 2017) J/ApJ/854/12 : 16yrs of radial velocity measurements of S0-2 (Chu+, 2018) J/A+A/616/A12 : Gaia DR2 sources in GC and dSph (Gaia Collaboration+, 2018) J/AJ/156/126 : Stellar parameters from BACCHUS analysis (Jonsson+, 2018) Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 F12.6 d HJD Heliocentric Julian Date; HJD-2400000.0 14 A1 --- Filt Filter (u, g, r, i or z) 16- 21 I6 --- Image [205418/429045] DECam exposure number 23- 26 I4 s Exp [5/300] Exposure Time -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 7 I7 --- ID [392/9682206] Identification Number 9- 20 F12.6 d HJD Heliocentric Julian Date; HJD-2400000.0 22 A1 --- Filt Filter (u, g, r, i or z) 24- 29 F6.3 mag mag [14.43/23.15] Apparent (AB) magnitude in Filt 31- 35 F5.3 mag e_mag [0.01/0.3] Error in mag -------------------------------------------------------------------------------- Byte-by-byte Description of file: table4.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 7 I7 --- ID [392/9682206] Identification number 9- 17 F9.5 deg RAdeg [269.67/272.11] Right Ascension (J2000) 19- 27 F9.5 deg DEdeg [-30.99/-29.06] Declination (J2000) 29- 35 F7.5 d Per [0.336/0.982] Period 37- 47 F11.5 d HJD0 Heliocentric Julian date at maximum light; HJD0-2400000.0 (1) 49- 50 I2 --- o_umag [0/70] Number of umag observations 52- 55 F4.2 mag uamp [0.36/1.98]? The u-band amplitude 57- 62 F6.3 mag umag [17.34/22.68]? Mean CTIO/DECam (AB) magnitude in u band 64- 69 F6.3 mag uref [17.76/22.91]? u band magnitude at minimum light (m_ref_) (2) 71- 72 I2 --- o_gmag [0/72] Number of gmag observations 74- 77 F4.2 mag gamp [0.25/1.56]? The g-band amplitude 79- 84 F6.3 mag gmag [16.13/20.35]? Mean CTIO/DECam (AB) magnitude in g band 86- 91 F6.3 mag gref [16.44/20.76]? g band magnitude at minimum light (m_ref_) (2) 93- 94 I2 --- o_rmag [0/70] Number of rmag observations 96- 99 F4.2 mag ramp [0.19/1.23]? The r-band amplitude 101-106 F6.3 mag rmag [15.35/19.46]? Mean CTIO/DECam (AB) magnitude in r band 108-113 F6.3 mag rref [15.56/19.72]? r band magnitude at minimum light (m_ref_) (2) 115-116 I2 --- o_imag [0/92] Number of imag observations 118-121 F4.2 mag iamp [0.13/1.01]? The i-band amplitude 123-128 F6.3 mag imag [15.01/19.1]? Mean CTIO/DECam (AB) magnitude in i band 130-135 F6.3 mag iref [15.19/19.37]? i band magnitude at minimum light (m_ref_) (2) 137-138 I2 --- o_zmag [0/85] Number of zmag observations 140-143 F4.2 mag zamp [0.11/1.01]? The z-band amplitude 145-150 F6.3 mag zmag [14.78/18.78]? Mean CTIO/DECam (AB) magnitude in z band 152-157 F6.3 mag zref [14.95/19.01]? z band magnitude at minimum light (m_ref_) (2) 159-178 A20 --- OName OGLE identifier (OGLE-BLG-RRLYR-NNNNN) if any; in SIMBAD -------------------------------------------------------------------------------- Note (1): Epoch of zero phase ({phi}=0). Note (2): Fitted value at {phi}=0.65. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table5.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 3- 14 F12.6 deg RAdeg [269.64/272.14] Right Ascension (J2000) 17- 28 F12.6 deg DEdeg [-31.01/-29.05] Declination (J2000) 32- 39 F8.3 mag umag [-12.8/23.6] Mean (AB) magnitude in u band (1) 42- 49 F8.3 mag e_umag [0.003/94] Uncertainty in umag (1) 52- 59 F8.3 mag gmag [12.09/23.57] Mean (AB) magnitude in g band 62- 69 F8.3 mag e_gmag [0.002/0.19] Uncertainty in gmag 72- 79 F8.3 mag rmag [11.95/22.19] Mean (AB) magnitude in r band 82- 89 F8.3 mag e_rmag [0.002/0.2] Uncertainty in rmag 92- 99 F8.3 mag imag [11.78/21.68] Mean (AB) magnitude in i band 102-109 F8.3 mag e_imag [0.002/0.16] Uncertainty in imag 112-119 F8.3 mag zmag [11.22/21.41] Mean (AB) magnitude in z band 122-129 F8.3 mag e_zmag [0.002/0.15] Uncertainty in zmag 134-140 F7.2 mag r-z [0.2/1.9] Color Excess (reddening) in r-z -------------------------------------------------------------------------------- Note (1): Negative magnitude values and/or uncertainty values that exceed 10mags indicate a non-existent measurement in that passband. This is most common in the u band, which does not reach as faint as the others. -------------------------------------------------------------------------------- History: From electronic version of the journal ================================================================================ (End) Prepared by [AAS], Emmanuelle Perret [CDS] 26-Aug-2020