exoclock

WASP-21b (LOW)

Discovered by: Bouchy et al. 2010

The Star
Simbad
GAIA
2MASS		 WASP-21
DR2 2831084391023184128
J23095825+1823459
RA 23:09:58.2534 DEC +18:23:45.882
Parallax
3.841 mas		 P.M. RA
17.597 mas/y		 P.M. DEC
18.867 mas/y
MagV
11.55		 MagR
11.52		 MagI*
10.832		 MagJ
10.35		 MagH
10.085		 MagK
9.982
MagG
11.399		 MagGBP
11.744		 MagGRP
10.912
*Calculated from GAIA magnitudes.

Ephemeris - Verified True
Kokori et al. 2025
Mid-time
2458330.7238 ± 0.00015 BJDTDB
Period
4.32250611 ± 5.7e-07 days
Transit Parameters
Bouchy et al. 2010
Rp/Rs
0.104 ± 0.0018		 a/Rs
10.54 +0.15 -0.15
 i
88.8 +0.8 -0.7 deg
e
-		 ω
- deg
DepthR*
14.28 mmag		 Duration*
3.4 hours
*Calculated from the other parameters, using PyLightcurve.
**Adjusted based on the space observations.

Limb Darkening Parameters
Bouchy et al. 2010
Teff
5800.0 +100.0 -100.0 K
 Log(g)
4.2 +0.1 -0.1 cm/s2
 Fe/H
-0.46 +0.11 -0.11 dex
ExoClock Status
Observing Priority LOW
Minimum aperture 5.0"
Total Observations (Recent) 45 (7)
O-C -1.05 ± 0.37 minutes
ExoClock Observations (Recent) 29 (7)
Space Observations (Recent) 6 (0)
ETD Observations (Recent) 0 (0)
Literature Mid-times (Recent) 10 (0)
Kepler Rp/Rs -
TESS Rp/Rs 0.10149 ± 0.00052

WASP-21b


ExoClock Observations
Planet
Observation Date		 Observer
Observatory		 Telescope
Camera / Filter / Exp [s]		 O-C
minutes
WASP-21b (LOW)
2025-12-09		Paolo Arcangelo Matassa
P:M.P.H.R. Deep Sky (K81)		Ritchey Chretien 40cm-F5.3
CCD ICX453AQ / Lum / 60.0		0.29 ± 1.87
WASP-21b (LOW)
2025-12-05		Kohji Tsumura
Tokyo City University		Vixen VC200L
ZWO ASI 1600MM-PRO / R / 180.0		-5.18 ± 2.45
WASP-21b (LOW)
2025-12-01		Ed Mullen
Sycamore Canyon Observatory		Planewave CDK20
FLI ML4240BI / AstrodonExoPlanet-BB / 10.0		-3.64 ± 0.76
WASP-21b (LOW)
2025-11-26		Francesco Conti
Francesco Conti		Celestron C11
ZWO ASI533 pro / Clear / 60.0		5.79 ± 2.74
WASP-21b (LOW)
2025-11-26		Jordi González-Edo
Landete-Kea		C11
ASI 2600MM pro / Lum / 90.0		-0.41 ± 1.87
WASP-21b (LOW)
2025-10-18		Yves Jongen
Rasteau Observatory		Plane Wave CDK 17"
SBIG STXL 11002 / R / 120.0		-2.01 ± 1.17
WASP-21b (LOW)
2025-08-28		Paolo Arcangelo Matassa
P:M.P.H.R. Deep Sky (K81)		Ritchey Chretien 40cm-F5.3
CCD ICX453AQ / Lum / 90.0		2.8 ± 3.46
WASP-21b (LOW)
2024-11-15		Giancarlo Madiai
GMAD48		SC8
ASI 432 MM / Clear / 30.0		-2.66 ± 2.02
WASP-21b (LOW)
2024-11-02		Claudio Lopresti
Claudio Lopresti		Mak-Newton
CCD Sbig ST10xme / R / 240.0		-4.22 ± 1.87
WASP-21b (LOW)
2024-10-20		Yves Jongen
Rasteau Observatory		Plane Wave CDK 17"
SBIG STXL 11002 / Lum / 60.0		1.97 ± 1.14
WASP-21b (LOW)
2024-09-24		Yves Jongen
Rasteau Observatory		Plane Wave CDK 17"
SBIG STXL 11002 / R / 120.0		2.35 ± 1.28
WASP-21b (LOW)
2024-08-29		Anaël Wünsche
Observatoire des Baronnies Provençales		CDK Planewave 2
ZWO ASI6200 / R / 120.0		0.45 ± 0.92
WASP-21b (LOW)
2024-08-04		Miguel Ángel Álava Amat
Sarriguren		Meade SC 8"
Asi 1600 MM / Lum / 180.0		-1.98 ± 1.07
WASP-21b (LOW)
2023-10-10		Paolo Arcangelo Matassa
P:M.P.H.R. Deep Sky (K81)		Ritchey Chretien 40cm-F5.3
CCD ICX453AQ / Lum / 60.0		-2.71 ± 3.02
WASP-21b (LOW)
2023-09-06		Bryan Martin
Tiger Butte Observatory Remote		AG Optical IDK
ZWO ASI 294 / Clear / 120.0		3.41 ± 1.73
WASP-21b (LOW)
2023-09-06		Charles Miller
Miller Observatory		Meade 12" LX850
QHY268M / R / 40.0		-4.8 ± 1.73
WASP-21b (LOW)
2023-08-06		Eric Miny
BLOIS SOLOGNE ASTRONOMIE OBSERVATORY		Newton T305
QSI 683WS / Lum / 60.0		-2.29 ± 1.44
WASP-21b (LOW)
2023-07-16		Bryan Martin
Tiger Butte Observatory Remote		AG Optical IDK
ZWO ASI 294 / R / 120.0		-2.39 ± 1.73
WASP-21b (LOW)
2023-07-12		Paolo Arcangelo Matassa
P:M.P.H.R. Deep Sky (K81)		Ritchey Chretien 40cm-F5.3
CCD ICX453AQ / Lum / 60.0		-0.22 ± 2.16
WASP-21b (LOW)
2022-12-07		Martin Crow
Burnham Observatory		Celestron C9.25
SX694 mono / R / 120.0		-0.36 ± 2.16
WASP-21b (LOW)
2022-08-26		David Arnot
OSO PIRATE		PlaneWave Instruments CDK24 24 inch (610 mm) f/6.5 Corrected Dall-Kirkham Astrograph
FLI ProLine KAF-16803 / R / 45.0		3.74 ± 2.16
WASP-21b (LOW)
2022-08-26		Yves Jongen
Deep Sky Chile		Plane Wave CDK 17"
Moravian 4G / R / 120.0		-1.87 ± 2.88
WASP-21b (LOW)
2021-09-23		Yves Jongen
Rasteau Observatory		Plane Wave CDK 17"
SBIG STXL 11002 / R / 120.0		-1.48 ± 1.01
WASP-21b (LOW)
2020-10-07		Anaël Wünsche
Observatoire des Baronnies Provençales		CDK Planewave
SBIG STL11K / Clear / 120.0		-2.49 ± 1.15
WASP-21b (LOW)
2020-08-29		Nikolaos Paschalis
Nunki Observatory		Officina Stellare RILA 400
SBIG STXL 11002 / R / 60.0		0.47 ± 1.73
WASP-21b (LOW)
2020-08-17		Francois Regembal
HRTobs		Astrosib RC360
SBIG STX 16803 / Lum / 120.0		-4.55 ± 2.3
WASP-21b (LOW)
2020-08-04		Yves Jongen
Rasteau Observatory		Plane Wave CDK 17"
SBIG STXL 11002 / R / 120.0		2.97 ± 1.44
WASP-21b (LOW)
2016-10-20		Anaël Wünsche
Observatoire des Baronnies Provençales		CDK Planewave
SBIG STL11K / Clear / 120.0		0.74 ± 1.58
WASP-21b (LOW)
2013-08-28		Kaushkee Vats
UCLO		Celestron (C14)
SBIG STL6303E / R / 60.0		-4.69 ± 2.59

Space Observations
Planet
Observation Date		 Mission O-C
minutes
WASP-21b (LOW)
2022-09-29		TESS1.74 ± 0.81
WASP-21b (LOW)
2022-09-25		TESS0.77 ± 0.88
WASP-21b (LOW)
2022-09-21		TESS1.77 ± 0.76
WASP-21b (LOW)
2022-09-16		TESS0.56 ± 0.76
WASP-21b (LOW)
2022-09-08		TESS-0.17 ± 0.82
WASP-21b (LOW)
2022-09-03		TESS0.57 ± 0.73

Literature Mid-times
Planet
Observation Date		 Reference O-C
minutes
2018-09-21 Alderson et al. 2020 -0.45 ± 0.45
2017-09-22 Alderson et al. 2020 -1.53 ± 0.43
2017-09-10 Alderson et al. 2020 -0.16 ± 0.33
2013-09-22 Seeliger et al. 2015 0.27 ± 1.05
2012-09-11 Ciceri et al. 2013 2.3 ± 1.14
2012-09-11 Ciceri et al. 2013 1.28 ± 0.52
2012-09-11 Chen et al. 2020 0.69 ± 1.02
2012-08-16 Seeliger et al. 2015 -0.9 ± 1.66
2011-08-24 Seeliger et al. 2015 -1.76 ± 1.61
2008-10-03 Bouchy et al. 2010 -1.63 ± 3.17
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