J/MNRAS/519/2451 NGC 7006's RR Lyrae physical properties (Arellano+, 2023)
Detailed analysis of the variable star population in the globular cluster
NGC 7006.
Arellano Ferro A., Rojas Galindo F.C., Bustos Fierro I.H., Muneer S.,
Yepez M.A., Giridhar S.
<Mon. Not. R. Astron. Soc. 519, 2451-2465 (2023)>
=2023MNRAS.519.2451A 2023MNRAS.519.2451A (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, variable ; Photometry ; Optical ;
Positional data ; Abundances, [Fe/H] ; Magnitudes, absolute ;
Stars, diameters ; Effective temperatures ; Stars, distances ;
Stars, masses
Keywords: stars: variables: RR Lyrae - stars: veriables: general -
stars: variables: fundamental parameters -
globular clusters: individual: NGC 7006
Abstract:
A 5-yr CCD photometric VI time series of NGC 7006 is employed to
perform a detailed analysis of the known population of variable stars.
In the process, we have corrected inconsistent classifications, sky
coordinates and found 10 new cluster member variables. An independent
reddening estimate with a value E(B-V) = 0.08 ± 0.05 is made. Using
Fourier decompositions of RR Lyrae light curves and well-established
calibrations, the cluster mean metallicity and distance
[Fe/H]ZW = -1.53 ± 0.15 and 41.2 ± 1.4 kpc are estimated based on
an extended sample of cluster member RRab stars. Using the Gaia DR3
data, we performed an extensive membership analysis that leads to a
clean colour-magnitude diagram, and hence to the identification of
variables that are likely field stars, and to considerations on the
variable distribution in the horizontal branch (HB). A double-mode RR
Lyrae and three CW stars are discussed. The origin of CW stars from
precursors in the blue tail of the HB with very thin
(∼0.06 ± 0.01 M☉) envelopes is argued. Our models indicate
that the main-sequence predecessor of RR Lyrae stars had a mass of
0.82-0.85 M☉ and lost about 25-35 per cent of its mass during
the red giant branch events before settling in the HB some 12-13.5 Gyr
later.
Description:
The present work, focused on the globular cluster NGC 7006, is part of
the long effort to employ the variable and RR Lyrae stars light curves
as indicators of their physical parameters, via the Fourier
decomposition. As presented in section 2, we obtain NGC 7006 LCs from
2m IAO telescope (Indian Astronomical Observatory, Hanle, India
between October 5 2011 and June 27, 2015) with a FoV ∼ 10.1*10.1
arcmin^2. The data reductions were carried out with the DanDIA
pipeline and accurate photometry was achieved with DIA. Next, we
assign membership status and variable types (based on Gaia DR3 proper
motions, for 3316 point sources). The table3.dat presents all the
variable stars presently known in NGC 7006 and shows the basic
photometric and positional data and membership status. To complete,
the resulting time-series VI photometry for each variable star
obtained in this work is available in table2.dat.
Secondly, we focus only on RR Lyrae stars in our sample to study the
light-curve morphology related to some of fundamental physical
parameters of the star and of the cluster to which they belong, of
particular relevance being the metallicity or [Fe/H] and the distance.
We use Fourier decomposition of the V light curve in harmonics. The
table4.dat exhibits the Fourier coefficients and parameters of the V
light curves of RRab and RRc stars in the cluster. Then, the
table5.dat lists the computed physical parameters correlated to
Fourier coefficients and parameters (i.e see section 5 and 4 for more
details).
Objects:
----------------------------------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------------------------------
21 01 29.46 +16 11 16.4 NGC 7006 = 2MASX J21012946+1611164
----------------------------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 39 22943 Time-series VI photometry for the variable
stars observed in this work
table3.dat 107 83 *Photometric, positional and membership data of
variable stars in NGC 7006 in images FoV
table4.dat 110 57 Fourier coefficients of the V light curves of
RRab and RRc stars in NGC 7006
table5.dat 101 44 *Physical parameters of RR Lyrae stars computed
with Fourier and calibrations to correlate
--------------------------------------------------------------------------------
Note on table3.dat: The photometry of variable stars in the cluster's FoV were
critically studied and found that 10 of them are field stars. The population
of variables cluster members is dominated by variables of the RR Lyrae type
(51 RRab, 9 RRc and 1 RRd) but also includes 7 semi regulars SR, and 2 EBs.
Note on table5.dat: RRab stars weighted means for all parameters in table are,
[Fe/H]ZW = -1.53 ± 0.01 [Sun] and its σ = ±0.15 [Sun],
[Fe/H]UVES = -1.43 ± 0.01 [dex] and its σ=±0.20 [dex],
[Fe/H]Nem = -1.41 [Sun] and its σ =±0.33 [Sun],
MV = 0.597 ± 0.001 mag and its σ=±0.040 mag,
logTeff = 3.802 [K] and its σ =±0.020 [K],
log(L) = 1.660 ± 0.001 [L☉] and its σ=±0.016 [L☉],
D = 41.17 ± 0.22 kpc and its σ=±1.39,
M = 0.67 ± 0.01 M☉ and its σ=±0.18,
R = 5.61 ± 0.01 R☉ and its σ=±0.56 R☉ .
Next, for RRc stars weighted means for all parameters in table are,
[Fe/H]ZW = -1.79 ± 0.16 [Sun] and its σ = ±0.27 [Sun],
[Fe/H]UVES = -1.72 ± 0.21 [dex] and its σ=±0.27 [dex],
[Fe/H]Nem = -1.84 ± 0.10 [Sun] and its σ =±0.28 [Sun],
MV = 0.61 ± 0.01 mag and its σ=±0.07 mag,
logTeff = 3.853 [K] and its σ =±0.022 [K],
log(L) = 1.656 ± 0.004 [L☉] and its σ=±0.027 [L☉],
D = 39.49 ± 0.19 kpc and its σ=±2.22,
M = 0.55 ± 0.01 M☉ and its σ=±0.13,
R = 4.27 ± 0.02 R☉ and its σ=±0.57 R☉ .
--------------------------------------------------------------------------------
See also:
J/MNRAS/511/1285 : M14 (NGC 6402). Variable stars VI light curves
(Yepez+, 2022)
J/MNRAS/499/4026 : NGC 6254 variable stars VI light curves
(Arellano Ferro+, 2020)
J/MNRAS/488/3024 : Globular clusters members with Gaia DR2
(Bustos Fierro+, 2019)
J/MNRAS/452/727 : NGC 6229 variable VI light curves
(Arellano Ferro+, 2015)
J/MNRAS/413/1275 : VrI light curves of NGC6981 variables (Bramich+, 2011)
J/MNRAS/402/226 : NGC 5053 variables VrI light curves
(Arellano Ferro+, 2010)
J/MNRAS/298/525 : Stellar evolution models for Z = 0.0001 to 0.03
(Pols+ 1998)
J/A+A/312/111 : [Fe/H] from RR Lyrae light curves (Jurcsik+, 1996)
J/AJ/129/267 : RR Lyrae variables in NGC 5272 (Cacciari+, 2005)
J/AJ/117/286 : Photometry of variable stars in NGC 7006 (Wehlau+, 1999)
J/other/ApSS/361.175 : M5 RR Lyr and HB VI light curves (Arellano Ferro+, 2016)
V/150 : Updated catalog of variable stars in globular clusters
(Clement+ 2017)
II/183 : UBVRI Photometric Standards (Landolt 1992)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- ID Star identifier raw number as VNN (Star_ID)
5 A1 --- Filter [V I] Filter band used (Filter)
7- 19 F13.5 d HJD Heliocentic julian date epoch of mid-exposure
(HJD)
21- 26 F6.3 mag Stdmag Standard VI magnitude value in VI
Johnson-Kron-Cousins as expressed in equation
1 and 2 of the section 2.2 respectively for V
and I (mstd)
28- 33 F6.3 mag Instmag The instrumental magnitude as measured by the
2m IAO telescope (mins)
35- 39 F5.3 mag e_Instmag Uncertainty of the Instmag which also
corresponds to the error of the standard
magnitude Stdmag (σm)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- ID Star identifier raw number as VNN
5 A1 --- f_ID Flag for new variable star found in this work
(flagID)
7- 10 A4 --- Type The variable type (Type)
12- 13 A2 --- f_Type Flag for Bl as RR Lyrae with Blazhko effect
where their amplitudes correspond to the maximum
observed (FlagType)
15- 20 F6.3 mag Vmag ? The mean magnitude in V band ()
22 A1 --- f_Vmag Flag for values taken from CVSGC of Clement et
al. 2001AJ....122.2587C 2001AJ....122.2587C, Cat. V/150 (flag)
24- 29 F6.3 mag Imag ? The mean magnitude in I band ()
31- 35 F5.3 mag AV ? The extinction AV in V band (AV)
37 A1 --- f_AV Flag for values taken from CVSGC of Clement et
al. 2001AJ....122.2587C 2001AJ....122.2587C, Cat. V/150 (flagAV)
39- 43 F5.3 mag AI ? The extinction AI in V band (AI)
45- 53 F9.6 d P ? Period computed in this study (Pd)
55- 63 F9.6 --- Pwsn ? Period from variable star catalog of Wehlau et
al. 1999AJ....117..286W 1999AJ....117..286W, Cat. J/AJ/117/286
(PdWSN99)
65 A1 --- f_Pwsn Flag for value taken from Pinto & Rosin
1973MmSAI..44..255P 1973MmSAI..44..255P (flagPWSN99)
67- 75 F9.4 d HJD ? The heliocentric julian day (HJD-2450000.0)
(HJDmax)
77- 78 I2 h RAh Right ascension (J2000)
80- 81 I2 min RAm Right ascension (J2000)
83- 87 F5.2 s RAs Right ascension (J2000)
89 A1 --- f_RAs Flag for values taken from CVSGC of Clement et
al. 2001AJ....122.2587C 2001AJ....122.2587C, Cat. V/150 (flagRAs)
91 A1 --- DE- Declination sign (J2000)
92- 93 I2 deg DEd Declination (J2000)
95- 96 I2 arcmin DEm Declination (J2000)
98-101 F4.1 arcsec DEs Declination (J2000)
103 A1 --- f_DEs Flag for values taken from CVSGC of Clement et
al. 2001AJ....122.2587C 2001AJ....122.2587C, Cat. V/150 (flagDEs)
105-107 A3 --- Mem Membership status (Mem) (1)
--------------------------------------------------------------------------------
Note (1): Membership status are as follows:
Y = Member, 67 occurences in our sample
N = No member, 11 occurences in our sample
? = No proper motions available or dubious membership, 6 occurences
in our sample
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- ID Star identifier raw number as VNN
5- 8 A4 --- Type The variable type RRab with 52 sources and RRc
with 5 sources in our sample (Type)
10- 15 F6.3 mag A0 The Vmag intensity weighted mean that is the
best estimation of mean magnitude of the V light
curve (A0)
17- 21 F5.3 mag e_A0 Error of A0 (errA0)
23- 27 F5.3 mag A1 The first Fourier coefficient of the V light
curves (A1)
29- 33 F5.3 mag e_A1 Error of A1 (errA1)
35- 39 F5.3 mag A2 The second Fourier coefficient of the V light
curves (A2)
41- 45 F5.3 mag e_A2 Error of A2 (errA2)
47- 51 F5.3 mag A3 The third Fourier coefficient of the V light
curves (A3)
53- 57 F5.3 mag e_A3 Error of A3 (errA3)
59- 63 F5.3 mag A4 The fourth Fourier coefficient of the V light
curves (A4)
65- 69 F5.3 mag e_A4 Error of A4 (errA4)
71- 75 F5.3 --- phi21 Fourier phase parameter φ21 defined with
φij = jφi - iφj (φ21)
77- 81 F5.3 --- e_phi21 Error of phi21 (errφ21)
83- 87 F5.3 --- phi31 Fourier phase parameter φ31 defined with
φij = jφi - iφj (φ31)
89- 93 F5.3 --- e_phi31 Error of phi21 (errφ31)
95- 99 F5.3 --- phi41 Fourier phase parameter φ41 defined with
φij = jφi - iφj (φ41)
101-105 F5.3 --- e_phi41 Error of phi41 (errφ41)
107-110 F4.1 --- Dm ? Deviation parameter Dm value (Dm)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 A3 --- ID Star identifier raw number as VNN
5- 8 A4 --- Type The variable type RRab with 39 sources and
RRc with 5 sources in our sample (Type)
10 A1 --- f_ID These variables are not included in the
calculation of [Fe/H] since their Dm
parameter is larger than 5.0 (flagID)
12- 16 F5.2 [Sun] [Fe/H]ZW ? The iron abundance value in the scale of
Zinn & West 1984ApJS...55...45Z 1984ApJS...55...45Z ([Fe/H]ZW)
18- 21 F4.2 [Sun] e_[Fe/H]ZW ? Error of [Fe/H]ZW (err[Fe/H]ZW)
23- 27 F5.2 [-] [Fe/H]UVES ? The [Fe/H]ZW transformation as eq. 4 of
sect. 5.1 with UVES scale of Carretta et al.
2009A&A...508..695C 2009A&A...508..695C ([Fe/H]UVES)
29- 32 F4.2 [-] e_[Fe/H]UVES ? Error of [Fe/H]UVES (err[Fe/H]UVES)
34- 38 F5.2 [Sun] [Fe/H]Nem ? The value given by the calibration of
Nemec et al. (2013ApJ...773..181N 2013ApJ...773..181N) scale
([Fe/H]Nem)
40- 43 F4.2 [Sun] e_[Fe/H]Nem ? Error of [Fe/H]Nem (err[Fe/H]Nem)
45- 48 F4.2 mag VMag ? The absolute magnitude in V band (MV)
50- 53 F4.2 mag e_VMag ? Error of VMag (errMV)
55- 59 F5.3 [K] logTeff Derived effective temperature using Fourier
decomposition parameters (LogTeff)
61- 65 F5.3 [Sun] logL Derived luminosity using Fourier
decomposition parameters (LogL/L☉)
67- 71 F5.3 [Sun] e_logL Error of logL (errLogL/L☉)
73- 77 F5.2 kpc D Computed stellar distance using Fourier
decomposition parameters (D)
79- 82 F4.2 kpc e_D Error of D (errD)
84- 87 F4.2 Msun M Computed mass using Fourier decomposition
parameters (M/M☉)
89- 91 F3.1 Msun e_M Error of M (errM)
93- 96 F4.2 Rsun R Computed radius using Fourier decomposition
parameters (R/R☉)
98-101 F4.2 Rsun e_R Error of R (errR)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
and Armando Arellano Ferro, armando(at)astro.unam.mx
(End) Luc Trabelsi [CDS] 30-Jan-2026