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 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:
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FileName Lrecl Records Explanations
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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
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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
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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
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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 2016AcA....66..197H, [arXiv:1605.04906])
VCNN = from Montiel & Mighell, 2010, Cat. J/AJ/140/1500
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Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
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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)
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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.
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- CVSGGC CVSGGC designation (VNNN),
Clement et al., 2001AJ....122.2587C 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
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Acknowledgements:
Roberto Jose Figuera Jaimes, robertofiguera(at)gmail.com
(End) Patricia Vannier [CDS] 16-Jun-2016