YY Gem Photometry
Bruce Gary, Hereford Arizona Observatory
YY Gem is a pair of M dwarfs in a 19.5-hr
orbit that transit each other. Their radii are inexplicably
larger than model predictions, which is typical of M dwarfs.
This discrepancy has been explained by invoking magnetic
fields but observational support is lacking. During Jan
3-12, 2012, Dr. Hebb performed spectropolarimetric
observations of YY Gem in order to determine the magnetic
field strength and brightness distributions of both
components. At Dr. Hebb's request I assembled a team of
advanced amateurs and coordinated photometric monitoring
during her 10-day professional observing dates. The amateur
light curves are currently being used by Dr. Hebb to
constrain solutions for brightness distribution on the stars
(i.e., starspot maps). This web page is an archive of those
amateur observations, as well as unrequested follow-on
observations by amateurs whose curiosity was aroused by
unexpected results from the scheduled observations.
Links to Sections on This Web Site
Published light curves show that transit depths are about
the same for primary and secondary transits, both
transit depths decrease with wavelength and a
small out-of-transit (OOT) variation is present. Flaring
activity has been noted but not systematically studied. The
amateur observations of this investigation are higher
quality than all previous investigations; they have better
wavelength coverage (B- to z'-band), essentially continuous
multi-band monitoring during the 10-day observing period,
and additional frequent observations for more than one year.
identified as secondary a decade ago is now deeper
than the other transit. The
tentative explanation for this is that starspots at critical
longitudes have changed during the past decade. This
explanation has additional support from recent observations
(November, 2012) showing that the OOT pattern has changed
significantly during the past 8 months, as have the two
transit depths - which implies very dynamic starspot
activity! This, in turn, suggests that at least one of the
YY Gem components is magnetically active. Indeed, during the
mid-December, 2011 observations (for refining
observing procedures) flaring was
absent, but during the scheduled 10-day
intensive monitoring period (Jan 3-12, 2012) flaring
was very common. Because of these observations we have
confidence in identifying the 2011/12 deepest transit as the
historically identified "secondary" transit. This permits
the determination of a greatly improved ephemeris, accurate
to ~ 1 millisecond. It is anticipated that observations by
amateurs will continue throughout the 2012/13 observing
season for the purpose of monitoring OOT and transit depth
changes on a monthly basis.
Publication summarizing results: SAS
2012 also Sky&Tel article
about this pro/am collaboration
Summary of Results
Finder Image &
2069A Light Curves (another web
What's New? with
YY Gem photometry analysis (another web page)
Individual Light Curves
for Pre-10-day and Post-10-day (another web page)
Jumping Off Page
for 10-day Light Curves (another web
page) - this is the path for viewing all of the 10-day
intensive observing period light curves.
Science Goal (as described by Dr. Leslie
Hebb, Vanderbilt University (currently at University of
"I have observing time on the CFHT 3.6-meter telescope (Mauna Kea)
on January 4-13, 2012 to observe the well known M dwarf EB, YY
Gem. The project involves getting time series spectropolarimetric
observations of YY Gem which will allow us to measure the magnetic
field strength on the surface of the components of the binary. One
of the most compelling problems in stellar astronomy to appear in
the last decade is that the radii of M dwarf stars are larger than
models predict by about 5-10%. This is thought to be due to the
magnetic activity on the stars, but no one has yet been able to
confirm this. Thus, the goal of our project is to determine if and
how the magnetic fields affect the radii of the low mass stars at
the most fundamental level by actually measuring the magnetic
fields of stars in a bright, well studied EB that are known to
have enlarged radii. These would be the first magnetic maps of an
M dwarf EB with properties (mass, radius, Teff) that are so well
determined. In addition, these data will provide brightness maps
of the surface of the stars through a technique called Doppler
"The project requires coincident time series photometry so that we
can (1) rederive the stellar parameters by modeling the EB with
the star spot positions and brightness known from the
spectropolarimetry, and (2) determine small scale star spots
through eclipse mapping techniques if the photometry is good
enough. I need high precision photometry, and want observers to
observe in different bands so we can do the best possible
January 3-12 measurements it is important to document the OOT
shape and is attributed to star spots or other causes for
non-uniform brightness across the EB surface. Flares have been
observed (U-band), so we want to know if any flare activity is
occuring during the January observations. Good quality transit
and eclipse shapes will be used for constraining models of EB
sizes, shapes, orbits, limb darkening, etc.
The photometry LC observations are to be made at filter bands
B, V, Rc, Ic and g', r', i', z'. Each observer is assigned a
filter or filter sequence. Ideally, continuous coverage during
the 10-day observing period would have been useful, but a
reasonable compromise wais to try to get LC observations
for times that are observable in Europe, America and Asia. The observing
team provided coverage from Eastern Europe, Western Europe,
USA and Japan. If we had been lucky with the weather we could
have obtained continuous coverage for most of the 10-day
observing window. Dr. Hebb's observing
time began January 4, 05 UT and ended at January 13, 16 UT.
Coordinates, Magnitudes and
RA/DE = 07:34:37.3 +31:52:09, "observing season"
is centered on January 13.
V = 8.99, Ic ~ 7.10 (Leung & Schneider,
1978). J = 6.073, K = 5.236 -> B = 9.7, V = 8.4, Rc = 7.69, Ic =
7.05 (Warner & Harris, 2007). This and other determinations are
included in the table below.
|Ref Star #1
|Based on above
|10.917 ± 0.020
|9.947 ± 0.016
|9.419 ± 0.013
|8.988 ± 0.016
|+0.970 ± 0.026
|Conversions from all-sky BVRcIc
Jester et al (2005)
|10.409 ± 0.020*
|9.650 ± 0.030*
|9.459 ± 0.045*
|9.318 ± 0.045*
|Consensus (final in bold)
|10.409 ± 0.020*
|9.650 ± 0.030*
|9.459 ± 0.045*
|9.318 ± 0.045*
|8.267 ± 0.021
|7.688 ± 0.018
|+0.970 ± 0.026
I conducted an all-sky observation on 2011.10.28 using B, V,
Rc, Ic, g', r', i', z' filters. Eight Landolt star fields were
observed (60 stars), that included SDSS calibrated magnitudes (22
stars). More description is given at all-sky
calibration. g'r'i'z' mag's with * after SE are
conversions from BVRcIc (Jester
et al, 2005)
|Based on above
|10.451 ± 0.018
|9.062 ± 0.013
|8.156 ± 0.009
|+1.389 ± 0.023
|Consensus (final in bold)
|6.073 ± 0.0??
|5.236 ± 0.0??
Torres & Ribas, 2002 (TR2002) performed a comprehensive analysis
of YY Gem transit observations from 1925 through 1999 (a span of 73
years), consisting of 57 primary and 55 secondary transits.
They corrected Leung & Schneider, 1978 observations for a couple
presumed mistakes, and these revised transit times are included in
the TR2002 analysis. Their final ephemeris for primary transits is:
HJD = 2449345.112327(87) + E *
Brief Summary of
Here is a list of results from my "amateur analysis" of this work's
amateur photometric observations (as of 2012 Nov 9):
1) Transit depths for primary and secondary had reversed values
during the 2011/12 observing season compared with 1949 and 1971
observations (i.e., secondary transit depth is now greater).
2) Transit depths changed significantly 8 months later (2012
Oct/Nov); both depths decreased but the secondary is only slightly
greater than the primary depth .
3) Starspots in 2011/12 are significantly different from 1949 and
1971, based on out-of-transit (OOT) shapes.
4) Starspots changed significantly during the 8 months separating
the 2011/12 observing season and 2012 Oct/Nov, based on a doubling
of OOT amplitude of variation.
5) Flare activity was low in late 2011 but active in 2012 January.
It again appears to be low (2012 Oct 30 to Nov 2).
An article describing the amateur photometry observations and their
analysis was published (May, 2012) in the Proceedings of the
Society for Astronomical Sciences (SAS), and can be viewed
using the link in the Reference section of this web page (bottom of
A professional analysis is being performed by Dr. Leslie Hebb of
both the amateur photometry observations described here and
spectropolarimetric observations conducted with the CFHT 3.6-meter
observatory in Hawaii by Dr. Leslie Hebb. When this article is
published everything on this web page will be superseded.
Results in More
Sample Light Curve of Primary Transit (last one taken)
Latest LC of a primary transit, showing shape and a small OOT
variation. The previous LC was made 3.2 years earlier (2012.12.12)
and it was also 1.2 minutes "early" using the same ephemeris. Both
also have the same depth 530 & 528 mmag). The only thing
different is the OOT variation, which was greater near primary
transit in 2012 than 32015, implying that the starspots move in
I recently analyzed 48 transits made between 2011 October and 2012
November (a span of 1.1 year) by the amateur team that I coordinated
and have determined the following ephemeris:
BJD = 2455935.10364(2) + E * 0.81428310(31)
Using the TR2002 ephemeris (eqn 1, above) to predict 8093 epochs
ahead yields 2455935.09827(13). The present work has transits
occurring 7.7 ± 0.2 minutes later. This is statistically
significant, and it may be explained by a very different starspot
situation (as shown by the OOT shape and depth relationships). I
therefore am not willing to interpret the 8 minute discrepancy in
terms of an ephemeris revision; instead, I will suggest (below) that
this discrepancy is caused by a large starspot that affects primary
Transit Depths vs. Wavelength
Previous transit depth determinations (Kron, 1952 and Leung &
Schneider, 1978) showed depth decreasing with wavelength. For
example, the LS78 V-band depths are 610 and 543 mmag, with the
deeper depth being the primary. The present investigation also
shows depth decreasing with wavelength. However, a surprise awaited
Figure 1a (left panel). Transit depths for 2011 Oct-Dec
("2011") and 2012 Jan ("2012").
Figure 1b (right panel). Same transit depths as in left
panel, but also showing 1971 depths by LS78. Symbols "S"
and "P" are for 2012 Oct-Nov.
In the above figure the left panel tells the story that the
secondary transit is deeper than the primary one! This surprising
result puzzled us for several months. Dr. Hebb suggested that this
might be caused by starspot changes. This theory gains credibility
by the dramatic change in transit depths 8 months later, as shown by
the "P" and "S" symbols that are based on observations between 2012
Oct 30 and 2012 Nov 2. In just 8 months both transit depths
decreased, but the secondary transit depth decreased much more than
the primary one. As I suggest below, the recent decrease in
primary transit depth may be due to the growth of a large starspot.
Phase-Folded Light Curves for 2011 Oct to 2012 Jan
Here's an example for Ic-band, made before the 10-day January
Figure 2. Phase-folded LC for Ic-band, for all Ic-band
data in the archive (as of 2011.12.31). Notice that the secondary
transits is deeper than the primary.
Figure 3. Tentative fit to Ic-band transits.
Here's a folded LC for all g'-band observations:
Figure 4. g'-band folded light curve, derived using
assumption that "air mass curvature" at g'-band is -22
mmag/airmass for all dates. The OOT variation has a peak-to-peak
amplitude of 37 mmag.
Figure 5a. Same data as in previous plot, but scaled to
emphasize OOT variation. Assumes air mass curvature is -22
Figure 5b. Phase folded for 8 r'-band LCs.
Figure 5c. Phase folded for 10 i'-band LCs.
Figure 5d. Phase folded for 8 z'-band LCs.
Figure 6. Amplitude (1/2 of peak-to-peak) of
out-of-transit (OOT) variations.
Phase-Folded Light Curves for 2012 Oct - Nov
Joao Gregorio and I have resumed observing YY Gem at the beginning
of this observing season for the purpose of refining YY Gem's
period. To my surprise, the OOT shape and transit depths have
changed since the last observation 8 months earlier. Consequently I
plan on conducting g' and z' observations once a month, on 4
consecutive nights, for the purpose of monitoring starspot changes.
Joao is observing with a V-band filter. Here's the phase-folded
g'-band LC that so surprised me.
Figure 7. g'-band phase-folded light curve for 2012 Oct
30 to 2013 Jan 07. The OOT variation has a peak-to-peak amplitude
of 108 mmag (vs 36 mmag for 2012 January).
And below is the z'-band phase-folded LC from the same ? observing
Figure 8. z'-band phase-folded light curve. The OOT
variation has a peak-to-peak amplitude of ~ 45 mmag.
"Stay tuned" to this web page for monthly updates.
Starspot Model for 2012 Oct/Nov
Warning: I am an amateur, so you should assume that I'm
prone to making mistakes due to the shortcomings of any amateur
attempting something new that is rightly the reserve of
Since OOT minimum is at phase ~ 0.14 we can infer that a starspot is
located at a longitude that is nearest star center (as viewed from
Earth) for one of the stars at this phase. If OOT exhibits an
additional real fade near phase 0.68 (as suggested by the
g'-band phase folded LC, Fig. 7) then one of the stars must have a
starspot at a longitude corresponding to this phase. There is a
theoretical case for expecting starspots to be confined to
mid-latitudes (e.g., 45 degrees) for stars within a mass range that
includes M dwarfs (Granzer et al, 2000). Following TR2002, I
adopted an inclination of 86.3 degrees. I've created a really crude
model representing starspot affects, and if I allow the latitude of
both starspots to be constrained to between 40 and 50 degrees I get
the following solution:
Figure 9. g'-band OOT data averaged for 5% phase bins,
fitted by a 2 starspot model with latitude constrained to 40 - 50
degrees and temperature difference of 200 K.
Figure 10. Model image of g'-band starspot model
of previous figure (for 2012 Oct 30 to Nov 19)..
If Spot #1 is located on the star being eclipsed during the primary
transit, then according to this model the spot is large enough to
affect the primary transit depth and egress shape. Notice that the
flux from both stars begins to fade before primary ingress (phase ~
0.87, Fig. 9). Such a geometry will decrease primary transit
depth, and shift the mid-transit time to a later time. This, indeed,
is what we have observed (when adopting the high quality ephemeris
The z'-band phase-folded light curve for the same date region (~ Nov
1, Fig. 8) shows a smaller OOT variation. This is expected due to
the fact that a fixed starspot temperature difference will have a
smaller flux ratio (inside spot to outside spot) at z'-band than
g'-band. This illustrated using a black body Planck function plot
for photospheric temperature (3820 K, according to TR2002) and
starspot temperatures that are cooler by hypothetical amounts of 100
K and 200 K.
Figure 11. Black body Planck function showing flux for
star surface brightnesses of 3820 K (photospheric model) and two
hypothetical starspot temperatures.
This graph allows us to predict that starspot effects at z'-band
should be ~ 60% of their effects at g'-band (e.g., (1.00 - 0.79) ÷
(1.00 - 0.65)). Inspection of Fig.'s 7 and 8 shows that the ratio of
the OOT variation at z'-band is ~ 50% (55 mmag ÷ 105 mmag) compared
to the g'-band variation. The difference in variation is therefore
compatible with the starspot explanation.
Figure 12. z'-band phase-folded light curve for 2012 Oct
30 to Nov 19. The OOT variation has a peak-to-peak amplitude of 44
mmag (vs 18 mmag for 2012 January).
Prior to the 10-day intensive observing dates we observed for 56
non-overlapping hours. During this time only one small flare was
observed. This corresponds to a flare activity level of 0.2 ± 0.2
flares per nominal 10-hour observing session.
During the 10-day intensive observing dates we observed a total of
180 non-overlapping hours, during which 20 flares were detected.
Most of these hours consisted of observations by several observers
using different filters. This allowed for an analysis of flare
intensity versus wavelength. This corresponds to a flare activity
level of 1.1 ± 0.2 flares per 10 hours, which is a ~5-fold increase
in flare activity.
Here's an example of a light curve exhibiting a flare.
Figure 21. Light curve of 2012.01.06 by Srdoc, showing a
flare at 26.2 UT.
And here's a "zoom" of the flare event:
Figure 22. Expanded version of previous LC's flare
region, showing detail of the flare's rise and decay structure.
The flare rise is 2.6 minutes, from onset to peak, and the 1/2-life
decay rate is ~ 8 minutes.
The same flare was observed at a shorter wavelength by several
observers. Here's a Bs-band light curve:
Figure 23. Light curve of same date by Zambelli at a
shorter wavelength, Bs-band, showing the dramatically greater
flare intensity at short wavelengths.
Flare intensity is 660 mmag at Bs-band, versus the 150 mmag at
Rs-band. This was the second largest flare observed by us, and it
was feasible to measure intensity at the long wavelengths. The next
figure shows this flare's behavior at 7 filter bands.
Figure 24. 10 LCs of the flare date, with 7 showing the
flare and it's change with filter band.
Here's a plot of flare intensity versus wavelength:
Figure 25. When plotted on a log-log scale the flare
intensity varies in a linear manner with wavelength.
Figure 26. This flare occurred on the first of the 10-day
intensive observing dates, during secondary ingress. It's
intensity is ~ 900 mmag.
A level of high flare activity started sometime after December 29
and before January 3. It was maximum on January 3/4 and subsided
slowly throughout the 10-day of intensive observations. No flares
were observed on the last of the 10 days, January 13/14.
Dates Before and After 10-day Intensive Monitoring Run
Here's a list of all YY Gem observations before and after
the 10-day January intensively monitored observing run. (A
list of obserations made during the 10-day run can be found at
YYYY.MM.DD Duration Observer
Band Primary/secondary Depth
582 mmag , 1 small flare
(130 mmag) during egress
2013.01.07 11.8 hrs
585 mmag , 1 small flare
2012.12.13 10.2 hrs
mmag , 2 small flares
2012.12.12 10.4 hrs
mmag , no flare
2012.12.11 9.6 hrs
mmag , no flare
8.5 hrs Gary
575 mmag, 90
8.5 hrs Gary
5?? mmag, no
2.1 hrs Gary
2.1 hrs Gary
8.1 hrs Gary
539 mmag, no
8.1 hrs Gary
547 mmag, no
7.2 hrs Gary g'
mmag, no flares
mmag, no flares
6.1 hrs Gary g'
2012.10.31 7.1 hrs Gary g'
572 mmag, no flares
540 mmag, no flares
2012.10.30 6.7 hrs Gary
2012.04.07 4.3 hrs Gary i'
2 mmag No flare
2012.02.11 9.1 hrs Gary i'
secondary 580 ±
2 mmag No flare
2012.01.03 to 2012.01.17 Listing of 77 Light
Curves (multi-band, many observer) for 10-day intensive
2011.12.29 9.4 hrs Gary
8 mmag Flare 62 mmag
secondary 612 ±
7 mmag Flare 21 mmag
secondary 584 ±
7 mmag Flare 0 mmag
7 mmag Flare 0 mmag
2011.12.28 4.7 hrs
Srdoc Vs primary
2011.12.27 10.1 hrs Gregorio Ic primary
2011.12.27 9.6 hrs Srdoc Rs
2011.12.26 6.1 hrs Foote J Ic primary
2011.12.26 8.8 hrs Foote C Ic
secondary (& p)
2011.12.26 11.1 hrs Gary Ic
secondary (& p) 582 ±
2011.12.23 10.7 hrs Srdoc R+ primary
2011.12.23 7.3 hrs Garlitz Rs primary
2011.11.27 8.8 hrs Gary B
mmag BJDo = 5892.7610
Gary V primary
562 ± 10 mmag
BJDo = 5892.7613
9 mmag BJDo = 5892.7614
± 9 mmag
BJDo = 5892.7616
Gary z' primary
± 11 mmag BJDo
2011.10.28 4.5 hrs FooteC B
2011.10.28 FooteC Ic
2011.10.28 5.7 hrs Gary B
Gary V OOT
Gary Rc OOT
Gary Ic OOT
Gary z' OOT
2011.10.24 3.8 hrs FooteC Ic secondary
± 1 mmag
2011.10.24 3.7 hrs
± 1 mmag
2011.10.24 6.6 hrs Gary
± 1 mmag
2011.10.20 3.2 hrs FooteJ Ic secondary
2011.10.20 3.5 hrs Gary Ic
± 2 mmag
Note: The "OOT offset" from true can be used to assess
the feasibility of combining non-overlapping LC segments -
provided there is no real OOT structure. Previously published
LCs show OOT strutcture, so I don't know how useful it will be
to search for constancy of "OOT offset" values for each
observer/filter combination. A possible strategy for
overcoming this uncertainty is to compare "OOT offset" values
taken at the same phase (e.g., always straddling secondary
transit). Another possible strategy is to compare "OOT offset"
differences between observers for same LC segments.
Here's a precise secondary LC shape:
secondary transit (Ic-band).
Individual Light Curves
(a separate web page)
Image & Calibrated Magnitudes
Figure 28. YY Gem (red circle) and reference star #1
(green box) with all-sky solutions for B, V, Rc, Ic
magnitudes. The other stars have B,V,Rc,Ic magnitudes given in
the table on the right. This is an Rc-band image (median
combine of nine 3-sec exposures). FOV = 18 x 19 'arc, north
up, east left. Notice bright Castor, at V-mag 1.6, a mere 71
"arc away. The upward spike is due to "saturation bleeding"
whereas the pattern of fainter light in four directions is due
to "pixel edge reflections." In order to keep the downward
pixel reflections from contaminating the YY Gem sky background
annulus I've rotated the CCD assembly 10 degrees
In this section I'll describe what I've found "works
for me" when observing this challenging target.
YY Gem is 71 "arc from Castor at position angle 165 degrees.
There's a 7.4 magnitude difference, so Castor reflections are
capable of ruining the YY Gem sky background levels. I have
had good luck rotating my CCD assembly ~ 10 degrees
counter-clockwise (as viewed from behind). This rotation
caused a counter-clockwise rotation of the star field, and
thus moved YY Gem away from Castor's pixel reflection pattern
(see above image).
Because YY Gem is bright (V-mag ~ 9.1), unbinned observing
allows exposure times to be 4 times longer than 2x2 binning.
Even unbinned, with my 16-inch aperture my exposure times were
short: B = 4 sec, V = 2 sec, Rc = 3 sec, Ic = 4 sec, 5 sec.
Only one star is used for reference, Ref#1 in the above image,
and since it is fainter than YY Gem you only have to assure
non-saturation for YY Gem.
I've settled on an observing sequence consisting of 5 filters
in alternation, which allows for LCs to be derived for bands
B, V, Rc, Ic, z'. It's not necessary to alternate after just
one exposure per filter; I expose 5 images for each filter
before moving to the next.
I typically observe whenever a target is above 15 degrees
elevation. For an object at YY Gem's declination this means my
local hour (LHA) can range from -6.2 to +6.2 hours. For
observing sites with latitudes north of mine (+31.4 deg.) a
larger LHA range is possible (provided the mount permits it).
I have found that photometry is free of detectable sky
brightness systematics whenever the sun is below -11.5 degrees
(which is 55 minutes after sunset, for me). On January 6, for
example, YY Gem rises through 15 deg. EL 24 minutes after the
sun goes below -11.5 deg. EL, and observing is forced to end
due to the sun rising through -11.5 deg. EL when YY Gem is
still at +21 deg. EL. Thus, at my latitude the longest
observing session will be 11.5 hours (LHA from -6.0 hrs. to
+5.5 hrs.). On January 13 UT YY Gem is at EL +16 deg when the
sun is low enough beow the horizon to observe (LHA = -6.0
hrs.) and YY Gem is at +16 deg. EL when the sun becomes close
enough to the horizon to terminate observing (LHA = +6.0 hrs).
Incidentally, on Jan 9 the moon passes 13.5 degrees from YY
Gem. B-band will be affected the most on this date.
Data file submission format is the same as for PAWM, described
in the "Data File" section at: http://brucegary.net/WDE/WDtargets.htm#Submission_Data_Format
Not everyone uses Johnson-Cousins BVRcIc filters;
however, almost everyone has SBIG RGB filters. The SBIG B has
a slightly longer effective wavelength than the Johnson B (450
vs 440 nm), and it has a wider passband. The SBIG G has the
same effective wavelength as the Johnson V-band filter (540 vs
540 nm), but it has a wider passband. The SBIG R has the
same effective wavelength (640 vs 640 nm), but it has a more
square passband shape. Therefore, the SBIG G and R filters are
similar to the Johnson V and Cousins Rc filters, respectively.
The filter passbands are shown in the following graphs.
Figure 29. Filter passband shapes.
telescope system has a unique passband shape for every filter,
no matter how "standard" the filter is. This is due to
wavelength dependent transmission of SCT corrector plates,
focal reducers, CCD QE function and atmosphere quality. The
only way to know how close a "telescope system passband
response function" is of each filter to a standard filter
passband is to observe a field of calibrated stars and inspect
the relationship between instrumental magnitude difference
from true magnitude and star color. When the slope of this
scatter plot is zero, the effective wavelength is the same as
for the standard filter's passband effective wavelength. Here
are some examples of such plots for my telescope system.
Figure 30. All-sky star
color dependencies used for estimating effective bandwidth of
various filters (as described in the text).
Since my Ic star color
sensitivity is zero, it has the same effective wavelength as the
standard Ic passband. My B-band instrumental magnitudes are too
"bright" for red stars, so my B-band effective wavelength is
longer than the standard passband's effective wavelength. My V and
Rc effective wavelengths are shorter than the standard. A method
for using the star color sensitivity plots, above, to derive
effective wavelength for the filter in use. The details for this
are described at EWL.
To illustrate use of the derivation at the above link, consider
the slope for my B-band: dB/dC = +0.141 mag/mag. According to the
relationship derived at the link, for filters near B-band:
WLeff = 446 nm + 42 × StarColorSensitivity
According to this equation when I use my B-band filter the
telescope system's response function has an effective wavelength
of 452 nm. Similar equations exist for the other bands.
The need for determining star color sensitivity slopes for each of
the YY Gem observer telescope systems is something I'm currently
discussing with Dr. Hebb. ...
To summarize approximate effective wavelengths for the various
filters (2nd column includes my non-standard notation):
441 nm B (Johnson)
450 nm Bs (SBIG's B)
478 nm g'
540 nm V (Johnson)
540 nm Vs (SBIG's G)
620 nm r'
640 nm Rs (SBIG's R)
624 nm Rc
755 nm i'
800 nm Ic
910 nm z'
Here's the YY Gem observer list (name, location, E.
Longitude, LHA range, filter assignment, effective wavelength,
available filters in parentheses):
Ayiomamitis, Greece +024 deg -5.?
to +5.? hr SBIG's B 450 nm
Srdoc, Croatia +014 deg -5.0
to +5.0 hr SBIG's R 640 nm
(SBIG R, Baader long-pass
Gregorio, Portugal -009 deg -5.? to +5.?
hr V 540 nm
Gary, Arizona -110 deg -6.2
to +6.2 hr g'r'i'z' 478, 620, 755, 910 nm
Foote C, Utah -112 deg
-5.0 to +5.0 hr V & Rc 540 & 624 nm
Foote J, Utah
-112 deg -5.0 to +5.0 hr B
& Ic 441 & 800 nm
Garlitz, Oregon -118 deg
-5.? to +5.? hr SBIG's B 450 nm
Yada, Japan +133 deg
-6.? to +6.? hr SBIG's B 441 nm
(BV & SBIG's RGB)
Zambelli, Roberto +010 deg -5.? to +5.? hr
V & Bs 540 & 450 nm
(V, LRGB, Baader G)
Figure 40. Longitudes of YY Gem observability for
members of this project's observer team.
Figure 41. Data
of Leung & Schneider (1978) fitted by Torres & Ribas.
Notice that OOT is brightest just after primary transit and
faintest just after secondary transit.
Gary, Bruce L., Leslie H. Hebb, Jerry L. Foote,
Cindy N. Foote, Roberto Zambelli, Joao Gregorio, F. Joseph Garlitz,
Gregor Srdoc, Takeshi Yada, Anthony I. Ayiomamitis,
"Photometric Monitoring by
Amateurs in Support of a YY Gem Professional Observing Project," Society
for Astronomical Sciences, 2012 Conference Proceedings
& PDF document download link).
Granzer, T., M. Schussler, P. Caligari, K. G.
Strassmeier, 2000, A&A, 355, 1087.
Joy, A. H. ad R. F. Sanford, 1926, Ap. J., 64,
Moffett, T. J. and B. W. Bopp, 1971, AJ, 168,
L117-120 (flare activity).
Qian, Shengbang, et al, 2002, AJ, 124,
1060-1063 (ephemeris with E2-term for shortening period).
Torres, Guillermo and Ignasi Ribas, 2002, AJ,
5567, 1140-1165, link
(spectroscopic obsns, re-analysis of published LC tables,
WebMaster: B. Gary. This site opened: 2011.10.20. Last Update: 2013.02.06