II/362 i-band variability of YSOs (Sergison+, 2020)
Characterising the i-band variability of YSOs over six orders of magnitude
in timescale.
Sergison D.J., Naylor T., Littlefair S.P., Bell C.P.M., Williams C.D.H.
<Mon. Not. R. Astron. Soc. 491, 5035 (2020)>
=2020MNRAS.491.5035S 2020MNRAS.491.5035S
=2020yCat.2362....0S 2020yCat.2362....0S
ADC_Keywords: Clusters, open ; YSOs ; Photometry, SDSS
Keywords: open clusters and associations: individual: Cep OB3b -
stars: formation - stars: pre-main-sequence - stars: rotation -
stars: variables: T Tauri - accretion
Abstract:
We present an i-band photometric study of over 800 young stellar
objects in the OB association Cep OB3b, which samples timescales from
1 minute to ten years. Using structure functions we show that on all
timescales (tau) there is a monotonic decrease in variability from
Class I to Class II through the transition disc (TD) systems to Class
III, i.e. the more evolved systems are less variable. The Class Is
show an approximately power-law increase (tau0.8) in variability from
timescales of a few minutes to ten years. The Class II, TDs and Class
III systems show a qualitatively different behaviour with most showing
a power-law increase in variability to a timescale corresponding to
the rotational period of the star, with little additional variability
beyond that timescale. However, about a third of the Class IIs show
lower overall variability, but their variability is still increasing
at 10 years. This behaviour can be explained if all Class IIs have two
primary components to their variability. The first is an underlying
roughly power-law variability spectrum, which evidence from the
infrared suggests is driven by accretion rate changes. The second
component is an approximately sinusoidal and results from the rotation
of the star. We suggest that the systems with dominant
longer-timescale variability have a smaller rotational modulation
either because they are seen at low inclinations or have more complex
magnetic field geometries. We derive a new way of calculating
structure functions for large simulated datasets (the "fast
structure function"), based on fast Fourier transforms.
Description:
We give tables of the i-band lightcurves of stars in the region, along
with structure functions and lightcurve statistics.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 33 41883 List of studied stars
tableb.dat 197 41774 Cep OB3b object properties and lightcurve
summary statistics
tablec.dat 131 191941 Cep OB3b low cadence structure functions
for 6845 stars
tabled.dat 131 81965 Cep OB3b high cadence structure functions
for 6850 stars
tablea.dat 71 25436190 Cep OB3b lightcurves for the 41883 stars
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See also:
J/MNRAS/403/545 : Young stars in Cepheus OB3b (Littlefair+, 2010)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1 I1 --- CCD [1/4] The CCD the star was observed with
3- 7 I5 --- StarID Star identifier within the CDD number (G1)
9- 10 I2 h RAh Right ascension (J2000)
12- 13 I2 min RAm Right ascension (J2000)
15- 20 F6.3 s RAs Right ascension (J2000)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000)
26- 27 I2 arcmin DEm Declination (J2000)
29- 33 F5.2 arcsec DEs [0/60] Declination (J2000)
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Byte-by-byte Description of file: tableb.dat
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Bytes Format Units Label Explanations
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1 I1 --- CCD [1/4] The CCD the star was observed with
3- 7 I5 --- StarID Star identifier number within CCD (G1)
9- 18 F10.7 mag imagClean ? Clean i-band magnitude from
Bell et al. (2013A&A...551L...7B 2013A&A...551L...7B)
20- 31 F12.9 mag i-ZClean ? Clean i-Z colour from
Bell et al. (2013A&A...551L...7B 2013A&A...551L...7B)
33- 35 I3 --- Npts Number of good lightcurve points (2)
37- 48 E12.10 mag AH68 ? Half the magnitude range covering 68
percent of observations for good
low-cadence datapoints
50- 59 F10.7 mag magMed ? Median magnitude for good low-cadence
datapoints
61- 70 F10.7 mag magMean ? Mean magnitude for good low-cadence
datapoints
72- 83 E12.9 --- rchi2 ? Reduced chi-squared about weighted mean of
good datapoints
85- 97 E13.10 mag uncMean Mean uncertainty for all unflagged
datapoints
99-108 F10.7 mag magMed2004 ? Median magnitude from 2004 data for
unflagged datapoints
110-119 F10.7 mag magMed2005 ? Median magnitude from 2005 data for
unflagged datapoints
121-130 F10.7 mag magMed2007 ? Median magnitude from 2007 data for
unflagged datapoints
132-141 F10.7 mag magMed2013 Median magnitude from 2013 data for
unflagged datapoints
143-145 A3 --- Cl Class (I, II, TD, III or LPS)
147-152 F6.3 d Per ? Period from Littlefair et al.
(2010, Cat. J/MNRAS/403/545)
154-159 F6.3 mag R-HaClean ? Clean R-Halpha colour from Littlefair et
al. (2010, Cat. J/MNRAS/403/545)
161-178 F18.14 deg RAdeg Right ascension (J2000.0) from Littlefair et
al. (2010, Cat. J/MNRAS/403/545)
180-197 F18.15 deg DEdeg Declination (J2000.0) from Littlefair et
al. (2010, J/MNRAS/403/545)
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Note (2): i.e. unflagged datapoints with positive flux and uncertainty less
than 0.2 mags
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Byte-by-byte Description of file: tablec.dat tabled.dat
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Bytes Format Units Label Explanations
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1- 17 E17.11 d Tau Timescale in days
19- 32 E14.10 --- Snett Structure function (SF) after removal of
photon and instrument noise
34- 46 E13.10 --- e_S Uncertainty in S and Snett
48- 60 E13.10 --- S Structure function (SF) including photon and
instrument noise
62- 74 E13.10 --- b_SLPS 16th percentile LPS SF at median flux MedFlux
76- 88 E13.10 --- SLPS Mean local photometric standard (LPS)
structure function (SF) at median flux MedFlux
90-102 E13.10 --- B_SLPS 84th percentile LPS SF at median flux MedFlux
104 I1 --- CCD [1/4] The CCD the star was observed with
106-110 I5 --- StarID Star identifier number within CCD (G1)
112-124 F13.7 --- MedFlux Median flux
126-128 A3 --- Cl Class (I, II, TD, III or LPS)
130-131 A2 --- FLAG [OO OU] Set to OU if SNett<e_S, else OO
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Byte-by-byte Description of file: tablea.dat
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Bytes Format Units Label Explanations
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1 I1 --- CCD [1/4] The CCD the star was observed with
3- 7 I5 --- StarID Star identifier within the CDD number (G1)
9- 26 F18.13 d BJD Mid exposure (BJD-2450000)
28- 39 F12.8 mag imag Sloan i-band magnitude
41- 54 E14.11 mag e_imag Uncertainty in imag
56- 57 A2 --- Qual [BCEFGHILNORS] Quality flag (2)
59- 63 A5 --- NegFlux [false/true ] Set true if flux is negative
65- 71 I7 --- Run INT run number
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Note (2): Quality flag, second character is the meaningful one.
O = O.K. (clean detection)
B = Background fit failed
C = Large relative transparency correction (cloudy)
E = Too close to CCD edge
F = Flagged pixel
G = Poor seeing
H = poor profile correction in the optimal photometry reduction
I = Ill-determined background
L = a star has been identified with counts above the pixel linearity
limit on the CCD during the pixel flagging procedure
N = Non-stellar
R = Uncalibrated region of CCD
S = Saturated
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Global notes:
Note (G1): From Littlefair et al. (2010, J/MNRAS/403/545),
unique only within each CCD.
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Acknowledgements:
Tim Naylor, timn(at)astro.ex.ac.uk
(End) Patricia Vannier [CDS] 06-Nov-2019