Principal Investigator Email Address
boekel@mpia.de
Estimated Total Execution Time (hours, including overheads)
5.0
General Description
This README is valid for programmes 084.C-783(A+B) and 084.C-789(A+B),
which comprise
a monitoring programme of the T Tau system at near- and mid-infrared wavelenghts
with NACO and VISIR (084.C-0783), and and optional TOO programme perfoming the same
observations with denser time sampling in case strong variations are detected during
the normal monitoring campaign (084.C-0789). The main monitoring programme 074.C-0783(A+B),
consists of "monthly monitoring" for the whole of P84 (except for march probably,
since the
source will be at high airmass already at the very beginning of the night), and
two months
of more intensive "weekly" monitoring (preferably november+december).
intro and some numbers:
The T Tau system consist of at least 3 stars with circumstellar disks: the optically
visible
Northern star "T Tau N", and the infrared companion "T Tau S" (~0.7 arcsec south
of T Tau N),
which itself is a close binary consisting of "Sa" (with ~2.2 Msun about equally
massive as
T Tau N) and "Sb" (~0.7 Msun). T Tau S has been strongly variable over the last
nearly 2
decades, and Sa is the prime source of variability, having shown variations with
a total
amplitude of >4 mag at 2.2 micron, and >2 mag at 12-13 micron. Sb is variable
as well, but
on a much lower level (RMS~0.2 mag at 2.2 micron). T Tau N has not shown substantial
infared
brightness variations and can thus be used to define the absolute flux scale in
imaging
observations in which relative photometry between N-Sa-Sb (for NACO) or between
N-S (for
VISIR, which does not spatially separate Sa-Sb) is performed. In an absolute sense,
the
fluxes to be expected are:
T Tau N: K=5.52, F(12.8)=8.2 Jy
Sa: total amplitude K=6.0-10.5, F(12.8) 5-25 Jy
expected in P84 K>8.5, K<10.5, F(12.8) 5-15 Jy (rough guesses)
Sb: K~8.6+/-0.2 (RMS), F(12.8) ~2 Jy
the purpose of this programme:
We will monitor the photometric variations of the T Tau system in the whole near-
to
mid-infrared region, with (near) simultaneous imaging with NACO and VISIR. The goal
is to accurately chart the color-brightness behavior of the Sa component. This allows
detailed modeling of the variability mechanism and can distinguish between apparent
brightness variations due to variable extinction as claimed in the literature, and
intrinsic luminosity variations due to variable accretion as we suggest.
Additionally, we will (quasi-)simultaneously monitor the Bracket gamma emission
lines
in Sa and Sb. This provides a critical and independent measure of the accretion
activity
in both sources.
The NACO observations spatially separate all 3 components, the VISIR observations
resolve
N-S but not Sa-Sb). Sa is the main variable source and it dominates the VISIR flux
of
T Tau S at all times. In the NACO observations, Sa may be substantially fainter
than Sb during P84, though it is not excluded that Sa is the brighter component
of the
southern pair during some epochs in P84.
The NACO and VISIR observations should be performed as close in time as possible,
whenever possible during the same night.
The whole P84 campaign consists of two programmes:
1) 084.C-783(A) NACO, 084.C-0783(B) VISIR:
the "monitoring" programme which consists of monthly observations during
the whole of P84 (6 observations), +denser (weekly) sampling during
two months (6 additional observations).
November+Dezember?
2) 084.C-789(A) NACO, 084.C-0789(B) VISIR:
the (optional) TOO programme, which comes into action in case rapid,
substantial variations are detected during the "intensive, weekly
monitoring". We will then trigger a more intense monitoring, with
one observation every 1-2 days.
The TOO part will be triggered according to the brightness evolution of Sa
in the NACO data.
Waiver Requests
We requested a waiver to use the NeII_2 filter instead of the NeII filter that was requested in phase 1.
Critical Observing Condition Constraints
none other than given in the OBs
Time-Critical Aspects
This "normal monitoring" part of our programme (as opposed to the TOO part, 084.C-0789(A+B)), consists of a "monthly" NACO+VISIR observation for the whole of P84, and a "weekly" NACO+VISIR observation for 2 months during this period (preferably november+december). We have not put explicit observing epochs in the "time intervals" fields, on the one hand to allow more flexibility (easier to be executed) without allowing a schedule that is not what is intended. For example, if we were to put the entire month in the time interval field for each observation in the monthly monitoring (i.e. allowing maximal flexibility), it would in principle be possible to do one observation on january 29 and the next on february 2, and the one after that on march 28 - obviously that is not what we want, but each time there may be different people on the mountain and when looking only at the time interval info in the OB, they would have no way to tell that this is not what is intended. In fact, it would be perfectly consistent with the "request" by the user! Our programme thus requires some active administration by the observatory staff. For both the "Monthly" and "Weekly" part of the monitoring programme, it is not needed to have the observations interspaced by exactly one month or exactly one week. Intervals of 1 month +/- 1 week, and 1 week +/- 2 days are a good guideline and allow for a reasonably relaxed schedule. It is much more important, that the near- and mid-infrared (NACO and VISIR) observations of each epoch are performed (quasi-) simultaneously, whenever possible during the same night. If, for example, practical issues on the mountain make it impossible to perform "simultaneous" NACO/VISIR observations during the week T Tau "is due", whereas this can be done one week later, then it is better to postpone the observations to that time. Scientifically, there is no preference for when to do the 2 months of weekly monitoring - we don't know when (and whether, for that matter) Sa will show strong photometric variablity. From a practical point of view, we prefer the "November+December" period, as Taurus is optimally visible then, and it leaves time for data analysis prior to proposal deadlines.
Special Execution Requirements
A note on the filter choice for the VISIR imaging/aqcuisition: The possibly somewhat onorthodox filter choice in the acquisition template (the B9.7 filter) was motivated by data that we recently analyzed, which suggests that the depth of the silicate absorption feature in T Tau S may vary with its overall brightness. By measuring at 9.8 micron (center of the silicate feature) and 13.0 micron (continuum red-ward of the feature), we are able to investigate another aspect of variability of T Tau S "for free". According to the sensitivities listed on the VISIR webpage for this filter (9 mJy for a 10-sigma detection in 1 hour of integration), we should detect T Tau N with >1000 sigma in the prescribed 90s integration, and T Tau S at somewhere between 250 and 700 sigma (depending on its actual brightness during the observation epoch). Since we are doing only imaging, and no sub-pixel accuracy is required for the acquisition, we deem this is more than sufficient. Should, after the "blind pointing" of UT3 in the acquisition, not all 4 of the source images in the acquisition image be useful since some fall onto bad pixels, this is no disaster. Part of those data will still be useful, and even if a few entire epochs are "lost" we still have a number of other epochs. We will very likely be lucky enough, though, such that most or even all epochs yield useable data in the acquisition image. We will do a relative photometric calibration, using the (non-variable) T Tau N as our "standard star". If possible (but this is not a must, of course), it would be great if the B9.7 filter was also used in the acquisition of the photometric standard that is part of the normal calibration plan (should be essentially as good as any of the filters normally used, even though the background is a bit higher than in other filters since part of the filter has the ozone feature in it). This would yield a PSF reference and an independent absolute flux calibration "for free".
Special Calibration Information
Standard calibration (standard star that serves as photometric calibrator and PSF reference) is sufficient.
ToO Information
ToO Activators List
Is this a Pre-imaging run ?
false
Pre-imaging Requirements
Source(s) of Pre-imaging
Pre-imaging sources not listed above
Do all your OBs comply with the instrument-specific requirements listed on the instrument-specific Phase 2 web page ?
If this is a pre-imaging run, did you select PRE-IMAGING for the Observing Category for each Observing Template ?
N/A
Do all your finding charts comply with both the general and instrument-specific Phase 2 Web Pages ?
If you submitted OBs for standard stars, did you specify the magnitude and spectral type of all standard stars in the OBs ?
N/A
Have you included OBs for any calibrations that you need but which are not part of the Calibration Plan ?
N/A
If you are observing Moving Targets, have you attached suitable ephemeris files to your OBs?
N/A
If you have preferences which OBs should be executed first, did you make use of the User Priority field in the OBs ?
N/A
If this is a run that requires coordinated observations with other facilities, did you give proper instructions in the Time-Critical Aspects Section ?
If the provided finding chart is at a different wavelength than the observations, did you clearly describe in the README file how to identify the target?
Did you specify a guide star brighter than V=12mag within a field of r=5arcmin around the science target?