CCD VRI photometry of the old open cluster NGC 7142
Photometry of 2194 stars in the field of the open cluster NGC 7142 in VRI filters was performed to search variable stars. Eleven probable variable stars were found using robust median statistics. We separated probable cluster members using proper motions from UCAC3 and our photometric diagrams. Also...
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Головна астрономічна обсерваторія НАН України
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| Zitieren: | CCD VRI photometry of the old open cluster NGC 7142 / A.F. Punanova, A.V. Loktin, V.V. Krushinsky, A.A. Popov // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 1. — С. 11-14. — Бібліогр.: 15 назв. — англ. |
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irk-123456789-1190962017-06-05T03:03:59Z CCD VRI photometry of the old open cluster NGC 7142 Punanova, A.F. Loktin, A.V. Krushinsky, V.V. Popov, A.A. Photometry of 2194 stars in the field of the open cluster NGC 7142 in VRI filters was performed to search variable stars. Eleven probable variable stars were found using robust median statistics. We separated probable cluster members using proper motions from UCAC3 and our photometric diagrams. Also we used our VRI photometry and JHK photometry from 2MASS to improve the age and the reddening for the cluster assuming the distance 1683 pc from WEBDA database. 2012 Article CCD VRI photometry of the old open cluster NGC 7142 / A.F. Punanova, A.V. Loktin, V.V. Krushinsky, A.A. Popov // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 1. — С. 11-14. — Бібліогр.: 15 назв. — англ. 2227-1481 http://dspace.nbuv.gov.ua/handle/123456789/119096 en Advances in Astronomy and Space Physics Головна астрономічна обсерваторія НАН України |
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Photometry of 2194 stars in the field of the open cluster NGC 7142 in VRI filters was performed to search variable stars. Eleven probable variable stars were found using robust median statistics. We separated probable cluster members using proper motions from UCAC3 and our photometric diagrams. Also we used our VRI photometry and JHK photometry from 2MASS to improve the age and the reddening for the cluster assuming the distance 1683 pc from WEBDA database. |
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Article |
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Punanova, A.F. Loktin, A.V. Krushinsky, V.V. Popov, A.A. |
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Punanova, A.F. Loktin, A.V. Krushinsky, V.V. Popov, A.A. CCD VRI photometry of the old open cluster NGC 7142 Advances in Astronomy and Space Physics |
| author_facet |
Punanova, A.F. Loktin, A.V. Krushinsky, V.V. Popov, A.A. |
| author_sort |
Punanova, A.F. |
| title |
CCD VRI photometry of the old open cluster NGC 7142 |
| title_short |
CCD VRI photometry of the old open cluster NGC 7142 |
| title_full |
CCD VRI photometry of the old open cluster NGC 7142 |
| title_fullStr |
CCD VRI photometry of the old open cluster NGC 7142 |
| title_full_unstemmed |
CCD VRI photometry of the old open cluster NGC 7142 |
| title_sort |
ccd vri photometry of the old open cluster ngc 7142 |
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Головна астрономічна обсерваторія НАН України |
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2012 |
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http://dspace.nbuv.gov.ua/handle/123456789/119096 |
| citation_txt |
CCD VRI photometry of the old open cluster NGC 7142 / A.F. Punanova, A.V. Loktin, V.V. Krushinsky, A.A. Popov // Advances in Astronomy and Space Physics. — 2012. — Т. 2., вип. 1. — С. 11-14. — Бібліогр.: 15 назв. — англ. |
| series |
Advances in Astronomy and Space Physics |
| work_keys_str_mv |
AT punanovaaf ccdvriphotometryoftheoldopenclusterngc7142 AT loktinav ccdvriphotometryoftheoldopenclusterngc7142 AT krushinskyvv ccdvriphotometryoftheoldopenclusterngc7142 AT popovaa ccdvriphotometryoftheoldopenclusterngc7142 |
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2025-07-08T15:13:13Z |
| last_indexed |
2025-07-08T15:13:13Z |
| _version_ |
1837092142985510912 |
| fulltext |
CCD VRI photometry of the old open cluster NGC 7142
A.F. Punanova∗, A.V. Loktin, V.V. Krushinsky, A.A. Popov
Advances in Astronomy and Space Physics, 2, 11-14 (2012)
© A.F. Punanova, A.V. Loktin, V.V. Krushinsky, A.A. Popov, 2012
Kourovskaya Astronomical Observatory of the Ural State University, 620083, 51 Lenin Ave., Yekaterinburg, Russia
Photometry of 2194 stars in the �eld of the open cluster NGC7142 in VRI �lters was performed to search variable
stars. Eleven probable variable stars were found using robust median statistics. We separated probable cluster
members using proper motions from UCAC3 and our photometric diagrams. Also we used our VRI photometry
and JHK photometry from 2MASS to improve the age and the reddening for the cluster assuming the distance
1683 pc from WEBDA database.
Key words: open clusters and associations: general, stars: variables: general, techniques: photometric
introduction
The old open cluster NGC7142 (ra = 21h45m09s,
dec = +65◦46′30′′ (2000), l = 105◦.347, b =
9
circ
.485) is located in Cepheus, a star-rich region of
the Milky Way. Few arcminutes aside one can �nd
young open cluster NGC7129 surrounded by a re-
�ecting nebula as a background, which partially ob-
scures some regions in NGC7142, therefore absorp-
tion in the �eld is irregular. Trumpler [12] de�ned
the cluster as II 1m. Subsequent work on the clus-
ter was reported by Hoag [5] (�rst color-magnitude
diagram (CMD) of the cluster), by Sharov [10] (in-
terstellar absorption, star counts) and by van den
Bergh[14], who paid attention to the similarities of
the CMD of NGC 7142 to those of the old open
clusters NGC188 and M67. Later van den Bergh
& Heeringa [15] estimated the distance modulus as
(m−M)0 = 12.5 and the age as lying between M 67
and NGC 188 ages. Crinklaw & Talbert [2] per-
formed the �rst CCD photometry and derived new
distance of (m−M)0 = 11.4±0.9 for the cluster, also
they found one variable star (V375Cep) and pro-
posed that stars of WUMa type could be found in
the cluster. Rose & Hintz [8] performed a search for
low amplitude short-period variables up to 15m in a
core region of NGC 7142. This paper presents the
new CCD VRI photometry of the cluster.
observations and data reduction
All observations were performed between Febru-
ary 2 and March 21, 2010 at Kourovskaya Astronom-
ical Observatory with Hamilton system telescope
MASTER II of MASTER Robotic Net [6]. The tele-
scope has two identical tubes with focal length =
1000 mm, aperture = 400 mm, �eld of view 2◦ × 2◦,
CCD ALTA U16M cameras, 4096×4096 px, and
scale: 1.8′′/px. Number of frames and exposure time
are presented in Table 1.
Astrometrical cross matching and aperture pho-
tometry of more than 500 frames were processed with
IRAF software package [11]. For the following re-
duction and di�erential photometry of 2194 stars in
the �eld of NGC7142 covering 30′ × 30′ a special
console program in C++ language was written. The
program executes algorithms described by Everett
& Howell [3]. Our photometrical errors for stars of
11m−15m are less than 0.05m in all bands. We trans-
formed our instrumental magnitudes to the Johnson-
Cousins VRI system using CCD photometry of our
�eld from [2, 4, 7]. Our instrumental magnitudes
system has a negligible dependence on magnitude
(slope=−0.00013±0.00012). The rms deviation from
standard system is ±0.035m.
Table 1: Observations
band nuber of frames exposure time, s
V 483 120
R 115 60
I 664 180
ccd vri photometry
JHK photometry from 2MASS Point Source Cat-
alogue was used to estimate reddening and eliminate
cluster members using CMD and Q-index diagram.
For the last one the sequence of non-reddened stars
∗PunanovaAnna@gmail.com
11
Advances in Astronomy and Space Physics A. F. Punanova, A.V. Loktin, V.V. Krushinsky, A.A. Popov
was calculated from the Table 1 of [13]. We also used
stars' proper motions from UCAC3 to exclude fore-
ground stars. The most part of stars in the core
region has µα = (−2.5 ± 6) mas/yr, µδ = (1 ±
6) mas/yr. Stars of core region (diameter=10′) inside
3σ interval of the proper motions having the identi-
cal reddening were determined as probable cluster
members. Probable cluster members are shown in
Fig. 1 where the found variable stars are denoted
with numbers. The best �t yielded reddening of
E(J − H) = 0.13 ± 0.05, the error was estimated
as a half-width of the cluster sequence.
Fig. 1: Q vs. J-H for cluster stars (points), variable stars
(asterisks); Q-index curve is shown with line with rect-
angles.
Fig. 2: MV vs. V-I: points denote cluster stars, solid and
dashed lines correspond to log age 9.4 and 9.6 respec-
tively.
The CMD of the probable cluster members is
shown in Fig. 2 with isochrones from [1] of loga-
rithm ages of 9.4 and 9.6 shifted with our estimation
of interstellar absorption and true distance modulus
12m.23 calculated using the cluster distance 1683 pc
from WEBDA database. The best �t of isochrones
gives estimation of logarithm age 9.55.
We made no attempts to estimate distance mod-
ulus due to short portion of cluster main sequence we
had in our disposition. Our estimations of age and
reddening appeared to be in good agreement with
previous ones.
search for variable stars
NGC7142 has two known variables. One of them
(V582Cep) lies out of our �eld of view, the other
(V375Cep) was observed successfully in V and I
bands. Photometry of stars in the �eld of the
open cluster NGC7142 in VRI �lters was performed
to search for variable stars. Eleven probable vari-
able stars were found using robust median statistics
(RoMS), described by Rose & Hintz [8]. One of the
stars is known as V375Cep. The statistics is repre-
sented by the equation:
RoMS =
1
N − 1
N∑
i=1
∣∣∣∣
mi −m
σi
∣∣∣∣ , (1)
where (N−1) is the number of degrees of freedom, N
is the number of observations, mi is the magnitude
of the i-th observation, m̂ is the median value (not
the average) of N observations, and σi is the error
per observation for a given magnitude mi de�ned by
an analytical error curve function.
Di�erential photometry was proceed for all the
suspect variable stars. For this aim for each vari-
able three comparison stars were used. The angu-
lar distance between variable and comparison star is
less then 30′′, magnitude di�erence is less then 0.5m,
rms deviation of comparison star magnitude changes
from 0.01m to 0.06m and equals to variable's one.
The periods were determined using the WinEfK
software package developed by Dr. V. P. Goran-
skij for Windows environment using La�er-Kinman
method. All the information about periods and
types of variable stars is presented in Table 2. Some
comments to the table are given below. All the
lightcurves are shown in Fig. 3.
All the spectral types were roughly determined
from Q-index diagram (see Fig. 1).
Object V375Cep is one of two known variable
stars in NGC7142 �eld, opened by G. Crinklaw and
F.D. Talbert [2]. Later R. Seeberger, R. Weinberger
and R. Ziener [9] using additional observations sug-
gested that the variable might be of WUMa type.
According to our observational data the star ap-
peared to be of EA type.
We suppose the star 1523 is of RR type due to
its period, amplitude, spectral type and location on
HR diagram, but it might be an eclipsing star of
EW type with period of 0.58 days.
12
Advances in Astronomy and Space Physics A. F. Punanova, A.V. Loktin, V.V. Krushinsky, A.A. Popov
Table 2: Variable stars.
ID ra dec Type max min System Period, Sp
days
958 21 44 54.74 +65 43 55.3 EA 16.13,15.50 16.53,15.90 V, I 0.9720 K0
995 21 46 03.07 +65 43 59.7 SR: 13.55,12.30,11.06 13.61,12.36,11,10 V, R, I 14:
1043 21 44 13.20 +65 45 01.3 EB/EW 15.75,15.15,15.05 16.20,15.60,15,50 V, R, I 0.4413 G3
1153 21 44 55.97 +65 45 49.9 SR: 15.51,14.33,13.75 15.71,14.53,13.86 V, R, I >20
1233 21 44 28.43 +65 46 36.5 EB/EW 17.75,16.70 18.75,17.70 V, I 0.3303
1400 21 43 47.85 +65 48 22.5 SR: 13.43,12.16,11.14 13.47,12.19,11.17 V ,R, I 20:
1459 21 44 29.61 +65 48 43.8 EA 14.70,14.73 15.15,15.10 R, I - F5
1523 21 45 15.15 +65 49 24.2 RR: 15.27,14.77,14.83 15.37,14.87,14.95 V, R, I 0.2900 F0
1561 21 46 08.90 +65 49 31.8 SR: 13.30,12.09,11.30 13.35,12.13,11.33 V, R, I 13:
1865 21 43 52.83 +65 54 27.7 SR: 14.23,12.80,11.68 14.35,12.90,11.73 V, R, I 20:
1880 21 45 10.69 +65 54 22.6 SR: 13.09,11.78,10.81 13.14,11.83,10.84 V, R, I >20
conclusions
We performed VRI photometry of 2194 stars in
the �eld of the open cluster NGC7142. According to
its CMD and color-color diagrams we determined the
log age of 9.55 and reddening E(J−H) = 0.13±0.05.
These results are in good agreement with the previ-
ous estimations. 11 variables were studied, 10 among
them were detected for the �rst time, 4 variables ap-
peared to be probable cluster members.
NGC7142 obviously contains blue straggler stars
(BSs). Our next task is to investigate high-resolution
spectra of brightest BSs of the cluster. For our vari-
able stars we intend to solve lightcurves of the eclips-
ing binaries we found and probably to search for low-
amplitude variables with periodogram analysis.
acknowledgement
This study was �nancially supported by the State
Agency for Science and Innovation of the Ministry
of Education and Science of the Russian Federation
(state contract No. 02.740.11.0249).
references
[1] Bertelli G., Bressan A., Chiosi C., Fagotto F. & Nasi E.
1994, A&AS, 106, 275
[2] Crinklaw G. & Talbert F.D. 1991, PASP, 103, 536
[3] Everett M.E. & Howell S. B. 2001, PASP, 113, 1428
[4] Hartigan P. & Lada C. J. 1985, ApJS, 59, 383
[5] Hoag A.A., Johnson H. L., Iriarte B. et al. 1961, Publ.
U. S. Naval Obs. 2d Ser., 17, 344
[6] Lipunov V., Kornilov V., Gorbovskoy E. et al. 2010, Ad-
vances in Astronomy, article ID 349171
[7] Magakian T.Yu., Movsessian T.A. & Nikogossian E.H.
2004, Astrophysics, 47, 519
[8] Rose M.B. & Hintz E.G. 2007, AJ, 134, 2067
[9] Seeberger R., Weinberger R. & Ziener R. 1991, Informa-
tion Bull. on Variable Stars, 3657, 1
[10] Sharov A. S. 1965, Soviet Ast., 8, 780
[11] Tody D. 1993, ASP Conf. Series, 52, 173
[12] Trumpler R. J. 1930, Lick Obs. Bull., 14, 154
[13] Turner D.G. 2011, RMxAA, 47, 127
[14] van den Bergh S. 1962, JRASC, 56, 41
[15] van den Bergh S. & Heeringa R. 1970, A&A, 9, 209
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Advances in Astronomy and Space Physics A. F. Punanova, A.V. Loktin, V.V. Krushinsky, A.A. Popov
Fig. 3: Lightcurves of the short-period variable stars which periods were determined precisely.
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