Survey Area and observing progress

 The VVV Survey

The VVV   Survey covers ~ 528 deg² containing ∼10^9 point sources and it includes multi-wavelength (ZYJHKs) coverage of the area as well as time monitoring in Ks band. The survey is scheduled to collect over 2000 hours of execution time.

The VISTA Telescope tile field of view is 1.501 deg², hence 196 tiles are needed to map the bulge area and 152 tiles for the disk. Adding some X and Y overlap between tiles for a smooth match, the area of our unit tile covered twice is 1.458 deg².

The VVV bulge area covers −10º < l < +10º and −10º < b < +5º, where the survey will give the most complete catalogue of variable objects in the bulge, with more than ∼10^6 variables. Chief among them are the RR Lyrae, which are accurate primary distance indicators, and well understood regarding their chemical, pulsational and evolutionary properties. Our survey of the RR Lyrae in the Galactic bulge will allow us to map its 3-D structure (as shown by Carney et al., 1995) and will provide key information on the age of its population, given that RR Lyrae stars are tracers of the old population (e.g., Catelan, 2004b, 2009, …).


VVV Survey Area Tile Numbers
VVV Survey Area Tile Numbers – Galactic Coordinates


In order to understand the Milky Way’s populations globally, it is necessary to survey the inner Galactic plane as well. Therefore, we will survey an adjacent region of the mid-plane and provide a Legacy Database and 3-D atlas of a large Population I (i.e. young and luminous stars) region. We have selected the region −65º < l < −10º and |b| < 2º, where star-formation activity is high and for which there will be complementary optical, mid-IR, and far-IR data from VPHAS+, the Spitzer, GLIMPSE and MIPSGAL surveys, and from the all- sky AKARI and WISE survey.


The Ks- band observations

The variability study in the bulge will be carried out in the Ks band down to ∼18 mag (signal-to-noise ≈ 3). The total exposure time for a VISTA tile field is 162 s. Our strategy yields about 30 deg² per hour, or 300 deg² per night. The combined epochs will reach Ks = 20 mag, which is three magnitudes fainter than the unreddened bulge main-sequence turn-off (MS turn-off), although the densest fields will be confusion-limited. However, applying both PSF fitting and image subtraction, we will recover the light curves of most objects down to Ks = 18 mag, even in moderately crowded fields. This is more than 3 mag fainter than the unreddened known RR Lyrae in the Galactic bulge. We expect to find RR Lyrae even in fields with AV = 10 mag.

If you are interested in the distribution of the individual Ks-band epochs, have a look at the next two plots.

The VVV eXtension:  VVVX

The observations for VVVX commenced on June 30, 2016, and will continue until 2019.

VVVX was granted a total of 2000 hours observing time, and cover a total of ~1700 sqr. degrees on sky and consists now of 1028 individual VIRCAM tiles.  In contrast to VVV the additional areas will be observed in J, H and Ks only.  The color coded areas shown in the figure below are:

I. Red: the original VVV area, for which we will obtain between 3 to 10 additional Ks-band observations, one to three per year, to extend the time line for PM studies.

II. Cyan: High/Low Bulge, extending the original bulge area to latitude +9.5º and lat -14.5º.

III. Green: Disk+20: extending the disk area from l=+10º to +20º, with b=-4.5º to +4.5º

IV. Blue: High/Low disk: extending the southern disk area from |b|=-2.28º to 4.5º. This will connect the VVV/VVVX area to the VISTA Hemisphere Survey, at least partially, given that VHS uses a RA/DEC alignment of the tiles, whereas VVV/VVVX is aligned along l,b. The longitude range for this area is l=230º to 350º. The combination of VVV/VVVX and the UKIDDS Galactic Plane survey will cover the entire galactic disk, over the full 360º longitude range!!!

V. Yellow: Disk+230: extend the inner galactic disk area (|b|<=2.28º) from l=295º to 230º.

The observations for areas II to V will include deep JHKs multi-color observations and multi-epoch observations in the Ks band, the exact number of epochs varying for the different area. We will give more details as soon as the final Survey Management Plan has been approved by ESO.

Color code for the area covered by the VVV eXtended; VVVX
Sky coverage of Cycle 2 Public Surveys with VISTA ©ESO

Progress in observations

All observations scheduled for the original VVV survey have been completed in 2015.
Starting in P97  (June 2016) ESO also started observing for VVVX. The following plots show the number of COMPLETED Ks-band observations  (aka ACCEPTED by ESO as within observing constrains ) at the given date (see headline of plots).  The upper number in each field gives the tile ID, whereas the lower number gives the number of Ks-band epochs, and includes the Ks-band observations carried out within the multi-color OBs.
The first plot refers to the areas I (VVV bulge), II (low/high bulge) and III (disk+20).
The inner disk tiles (region I and IV) are shown in the next plot.
 In addition the disk+230 area and the outer ranges of the lower (dl) and upper disk (dh)  area have been observed as well, although first observations started only in P100.
The progress in observations is shown in the plot below.
The different observing runs for VVV ( run: 179.B-2002 A,B,C,D,E,F,G,H,K,L) and VVVX (run: 198.B-2004(A),B) were all completed. There are two VVVX run currently open-  179.B-2004(C,D). Run 198.B-2004(C) was – like run 198.B-2004(A) an early submission to make use of observing time during P99 and P101 that could not be used  by other projects, due to  weather conditions. Run 198.B-2004(D) will include 150 h of observation of the outer southern disk, and is the first summer semester within the VVVx survey. The observations for this run have have started.
Completeness at 22012018:
198.B-2004(A): 2318 of 2318 OBs: 100%, or 202.6 of 202.6 h: 100 %
198.B-2004(B): 1779 of 1779 OBs: 100%, or 212.1 of 212.1 h: 100%
198.B-2004(C): 1893 of 1910 OBs: 99.1%, or 192 of 199.6h: 98.7%
198.B-2004(D): 40 of 1040 OBs: 3.8%, 3 of 149.6h: 2%
Upcoming observations
 P101, another winter semester will include 199h of new observations (run 198B-2004(E), as well as 23h to be spent on observing previously ‘D’ graded observations (run 198B-2004(F)). This means the data are not 100% within specifications, but repeating them will depend on further inspection. The 23 hours will allow us to repeat all grade D observations. Our argument for this was that the multi-color observations are only done once anyway, and that the new VVVx areas already get less Ks-band epochs than the original VVV, and we need every epoch we can get. Fortunately, ESO agreed with this  and granted the total time needed for this run.



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