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J/A+A/592/A120      Variable stars in NGC 6715           (Figuera Jaimes+, 2016)

Many new variable stars discovered in the core of globular cluster NGC 6715 (M54) with EMCCD observations. Figuera Jaimes R., Bramich D.M., Kains N., Skottfelt J., Jorgensen U.G., Horne K., Dominik M., Alsubai K.A., Bozza V., Burgdorf M.J., Calchi Novati S., Ciceri S., D'Ago G., Evans D.F., Galianni P., Gu S.H., Harpsoe K.B.W, Haugbolle T., Hinse T.C., Hundertmark M., Juncher D., Kerins E., Korhonen H., Kuffmeier M., Mancini L., Peixinho N., Popovas A., Rabus M., Rahvar S., Scarpetta G., Schmidt R.W., Snodgrass C., Southworth J., Starkey D., Street R.A., Surdej J., Tronsgaard R., Unda-Sanzana E., von Essen C., Wang X. B., Wertz O., (The MiNDSTEp Consortium) <Astron. Astrophys. 592, A120 (2016)> =2016A&A...592A.120F (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry Keywords: atmospheric effects - instrumentation: high angular resolution - globular clusters: individual: NGC 6715 (M 54) - methods: observational - stars: variables: general - stars: variables: RR Lyrae Abstract: We show the benefits of using Electron-Multiplying CCDs and the shift-and-add technique as a tool to minimise the effects of the atmospheric turbulence such as blending between stars in crowded fields and to avoid saturated stars in the fields observed. We intend to complete, or improve, the census of the variable star population in globular cluster NGC 6715. Our aim is to obtain high-precision time-series photometry of the very crowded central region of this stellar system via the collection of better angular resolution images than has been previously achieved with conventional CCDs on ground-based telescopes. Observations were carried out using the Danish 1.54-m Telescope at the ESO La Silla observatory in Chile. The telescope is equipped with an Electron-Multiplying CCD that allowed to obtain short-exposure-time images (ten images per second) that were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). The high precision photometry was performed via difference image analysis employing the DanDIA pipeline. We attempted automatic detection of variable stars in the field. We statistically analysed the light curves of 1405 stars in the crowded central region of NGC 6715 to automatically identify the variable stars present in this cluster. We found light curves for 17 previously known variable stars near the edges of our reference image (16 RR Lyrae and 1 semi-regular) and we discovered 67 new variables (30 RR Lyrae, 21 long-period irregular, 3 semi-regular, 1 W Virginis, 1 eclipsing binary, and 11 unclassified). Description: Observations were taken during 2013, 2014, and 2015 as part of an ongoing program at the 1.54m Danish telescope at the ESO observatory at La Silla in Chile that was implemented from April to September each year. table1.dat file contains the time-series I photometry for all the variables in NGC 6715 studied in this work. We list standard and instrumental magnitudes and their uncertainties corresponding to the variable star identification, filter, and epoch of mid-exposure. For completeness, we also list the reference flux, difference flux, and photometric scale factor, along with the uncertainties on the reference and difference fluxes. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 121 85 Ephemerides and main characteristics of the variable stars in the field of globular cluster NGC 6715 table1.dat 93 3651 Time series I photometry for all the variables studied in this work tableb1.dat 22 129 Cross-identification between the RR Lyrae variables listed by the CVSGGC, the variable star candidates from Montiel & Mighell and the OGLE RR Lyrae stars
See also: J/AJ/140/1500 : RR Lyrae variables in central region of M54 (Montiel+, 2010) J/AcA/64/177 : VI light curves of Galactic Bulge RR Lyrae (Soszynski+, 2014) Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 4 A4 --- VName Variable star ID (VNNN) 5 A1 --- Note [a] a: Epochs, periods, mean magnitudes, amplitudes, and classifications taken from OGLE database 7- 36 A30 --- OName Previously known ID assigned to the stars (1) 38- 39 I2 h RAh Right ascension (J2000) 41- 42 I2 min RAm Right ascension (J2000) 44- 49 F6.3 s RAs Right ascension (J2000) 51 A1 --- DE- Declination sign (J2000) 52- 53 I2 deg DEd Declination (J2000) 55- 56 I2 arcmin DEm Declination (J2000) 58- 62 F5.2 arcsec DEs Declination (J2000) 64- 75 F12.4 d Epoch ?=- Epoch used (HJD) 77- 88 F12.8 d Per ?=- Period measured in this work unless the variable is an OGLE star, in which case we use their period 92-101 F10.8 d e_Per ? rms uncertainty on Per 103-107 F5.2 mag Imag ?=- Median I magnitude 108 A1 --- n_Imag [d] d: Peak magnitude 110-113 F4.2 mag Amp(i+z) ?=- Peak-to-peak amplitude in the light curve (i'+z') 115-116 I2 --- N Number of epochs 118-121 A4 --- Type Classification of the variable
Note (1): Other names as follows: NNNNN = OGLE identifications of the form OGLE-BLG-RRLYR-NNNNN (Soszynski et al, 2014, Cat. J/AcA/64/177) O16 = variable star was discovered independently by Hamanowicz et al. (2016AcA....66..197H, [arXiv:1605.04906]) VCNN = from Montiel & Mighell, 2010, Cat. J/AJ/140/1500
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 4 A4 --- VName Variable star ID (VNNN) 6 A1 --- Filt [I] Observation filter 8- 20 F13.5 d HJD Heliocentric Julian date at mid-exposure 22- 27 F6.3 mag mag.s ?=0 Standard magnitude (I band) 29- 34 F6.3 mag mag.i ?=0 Instrumental magnitude (I band) 36- 40 F5.3 mag e_mag.i ?=0 Magnitude uncertainty (standard or instrumental) 42- 52 F11.3 s-1 Fref ?=0 Reference flux (I band) (in ADU/s unit) (1) 54- 64 F11.3 s-1 e_Fref ?=0 Reference flux uncertainty (in ADU/s unit) 66- 77 F12.3 s-1 DFlux Difference flux (I band) (in ADU/s unit) (1) 79- 86 F8.3 s-1 e_DFlux Difference flux uncertainty (in ADU/s unit) 88- 93 F6.4 --- p Photometric scale factor (1)
Note (1): Light curves for each star were constructed by calculating the total flux ftot(t) in adu/s at each epoch t from ftot(t)=fref+fdiff(t)/p(t) where fref is the reference flux (adu/s), fdiff(t) is the differential flux (adu/s) and p(t) is the photometric scalefactor (the integral of the kernel solution) Conversion to instrumental magnitudes was achieved using mins(t)=17.5-2.5log(ftot(t)) where mins(t) is the instrumental magnitude of the star at time t. Uncertainties were propagated in the correct analytical fashion.
Byte-by-byte Description of file: tableb1.dat
Bytes Format Units Label Explanations
1- 4 A4 --- CVSGGC CVSGGC designation (VNNN), Clement et al., 2001AJ....122.2587C, Cl* NGC 6715 SAW VNNN in Simbad 6- 16 A11 --- OGLE OGLE designation (RRLYR-NNNNN), Soszynski et al., 2014, Cat. J/AcA/64/177, OGLE BLG-RRLYR-NNNNN in Simbad 19- 22 A4 --- VC Montiel designation (VCNN), Montiel & Mighell, 2010, Cat. J/AJ/140/1500 [MM2010] VCNN in Simbad
Acknowledgements: Roberto Jose Figuera Jaimes, robertofiguera(at)gmail.com
(End) Patricia Vannier [CDS] 16-Jun-2016
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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