UKIDSS Science Verification

Steve Warren

UKIDSS began full survey operations on May 13, 2005, and the data taken in the observing block up to the end of June when the instrument came off again represents about 2% of the planned 7-year survey. Particular fields were targeted before the start of the survey for science verification purposes. These data have been pipelined and archived. A group of UKIDSS consortium astronomers are analysing this small dataset, and feeding back findings to the wide-field survey groups CASU (pipeline) and WFAU (archive), as a contribution to the shakedown of the system. Broadly speaking we are impressed with the results even at this early stage. We expect the science verification phase to be complete by the end of October, and the first data release of the May/June block to take place before the end of the year.

FIGURE 1: One of the "lost galaxies" of Virgo... Click on the image for the full 1400x1400 pixel (9.3x9.3 arcmin) image. Data extracted from just one of the four WFCAM arrays.

One of the science verification fields was a strip crossing part of the Virgo galaxy cluster. The colour image above is a composite of 40 second exposures in the YJK bands of the barred-spiral galaxy NGC4535. The field is 1400x1400 pixels in size, with a pixel scale of 0.4". North is up, East is to the left.

WFCAM synthetic photometry: First UKIDSS paper submitted

Paul Hewett¹, Steve Warren², Sandy Leggett³, Simon Hodgkin⁴

As alluded to in the previous section, the first observing season for UKIDSS has been completed, and the first data release will occur before the end of the year. A series of five baseline papers, which will provide the reference technical documentation for UKIDSS, is in preparation. These are:

1. Lawrence et al. (2006) describing the scope, layout, and broad science goals of the five surveys that make up UKIDSS
2. Casali et al. (2006) describing the Wide Field Camera, WFCAM
3. Hewett et al. (2005) characterising the photometric system of the survey
4. Irwin et al. (2006) providing the details of the pipeline, and
5. Hambly et al. (2006) describing the WFCAM Science Archive that will provide access to the images and object catalogues.

FIGURE 1: System response curves for the WFCAM ZYJHK filter set. Two curves are shown for each band. The lower curve is the total throughput of the system from above atmosphere to detector. The upper curve omits the effect of the atmosphere.

FIGURE 2: YJH 2-colour diagram illustrating how Y dwarfs might be selected. Key: BPGS O-K dwarfs filled/blue circles; M dwarfs open/green circles; L dwarfs filled/orange triangles; T dwarfs open/red triangles; model Y dwarfs filled/purple and open/purple squares; quasars 0 < z < 8.5 (in steps of 0.1) solid black line; H cool white dwarfs dotted black line; He cool white dwarfs dashed black line.

The aims of the photometry paper are similar to those of the paper by Fukugita et al. (1996) for SDSS i.e. to characterise as closely as possible the photometric system, and to synthesise colours of astronomical sources, as an aid to interpretation of the data. WFCAM has 5 broadband filters ZYJHK. The JHK filters have been manufactured to the MKO specification (Simons and Tokunaga, 2002), and so are expected to have negligible colour terms compared to the MKO standards. The Z and Y bands cover the wavelength ranges 0.83-0.925 micron and 0.97-1.07 micron respectively. This whole wavelength range is relatively little explored, with the notable exception of the Sloan Digital Sky Survey z band. This latter passband has an extended red tail, which includes significant atmospheric absorption near 0.95 micron. The WFCAM Z filter has a similar effective wavelength to the SDSS z filter, but a rectangular profile, while the new Y band aims to open up the region between Z and J.

Passband response functions have been computed by taken into consideration all wavelength dependent quantities, including atmospheric absorption, mirror reflectivity, filter transmission, and array quantum efficiency. Wavelength independent quantities are irrelevant for synthesising colours, but have been included by normalising the computed curves to the measured system throughput. The estimated final system throughput as a function of wavelength is shown in Fig. 1. We have used these transmission curves together with the spectrum of Vega of Bohlin and Gilliland (2004) to compute colours, offsets to the AB system, and colour equations for conversion between WFCAM bands and the SDSS z band, and the 2MASS JHK bands.

We have synthesised, and tabulate in the paper, colours of a wide range of astronomical sources as listed below:

• Stars, using the Bruzual, Persson, Gunn, and Stryker atlas, and additional published spectra of cool M stars.
• A large number of L (30) and T (22) brown dwarfs.
• Model very-cool brown dwarfs, cooler than T. It is expected that a new spectral class will appear at cool temperatures, possibly 600-400 K (the coolest brown dwarf known has an effective temperature of about 700 K). One of the goals of UKIDSS is to discover and characterise this population, termed Y dwarfs.
• Cool H and He atmosphere white dwarfs.
• Galaxies of a range of spectral types, and over a wide redshift range, using template spectra of the hyperz library (Bolzonella et al., 2000), and the atlas of Manucci et al. (2001).
• Model quasar spectra over the entire redshift range 0 < z < 8.5.

As an illustration of the results we show in Fig. 2 the YJH two-colour diagram for stars and quasars, that illustrates the potential of the Y band for detecting cool brown dwarfs. T dwarfs become blue in J-H and track up the stellar sequence in a JHK diagram. The Y-J colour pulls the T dwarfs (open triangles in the figure) down below the stars so they may be identified. Y dwarfs, shown as filled and open squares in the figure, for two different models, are expected to be blue in J-H, and possibly redder than T dwarfs in Y-J.

All the relevant tables from the paper, including response curves, and synthetic colours are available from the UKIDSS web site: www.ukidss.org. The photometry paper itself, Hewett et al. (2005), is also available.

REFERENCES:
Bohlin, R., Gilliland, R., 2004, AJ, 127, 3508
Bolzonella, M., Miralles, J.-M., Pello, R., 2000, A&A, 363, 476
Fukugita, M, et al., 1996, 1996, AJ, 111, 1748
Mannucci, F., 2001, MNRAS, 326, 745
Simons, D., Tokunaga, A., 2002, PASP, 114, 169

Polarimetry at UKIRT

Chris Davis

Figure 1: An image of the young star L1551-IRS5 with polarisation vectors overlayed. Data obtained with UIST, reduced with ORAC-DR, and displayed with the Polarimetry Toolbox in GAIA.

UKIRT has a long tradition of dual-beam polarimetry with its facility instruments and the IRPOL unit, which was originally supplied by the University of Hertfordshire. This tradition continues, most recently with the expansion of spectro-polarimetry options for UIST.

In early 2005 a second Wollaston prism was purchased and installed in UIST's second grism wheel. With a prism in both wheels, spectro-polarimetry is now available with all installed grisms; at low spectral resolution (R~1000) over a broad wavelength range with the IJ, JH, HK, KL and M grisms, and at higher resolution (R~3000) with the short- and long- grisms in the J, H, K, and L bands.

Our goal has also been to provide automated yet reliable pipeline software for the reduction and assessment of polarimetry data in real time at the telescope. While stationed in Hilo, Malcolm Currie developed a suite of ORAC-DR recipes to reduce imaging polarimetry data. Images reduced with these recipes are bad-pixel masked, dark subtracted and flat-fielded before e- and o-beam sub-images are extracted and processed to produce images in the Stokes I, Q, and U vectors, the percentage polarisation P and position angle theta (TH), as well as FITS binary-table catalogues of the binned and culled polarisation data. The DR ultimately displays an image with vectors overlayed showing the percentage polarisation and position angle across the image. Additionally, with the polarimetry toolbox in GAIA, observers are able to bin, rotate, and selectively display vectors over a carefully-scaled image. The data in Figure 1 were reduced with orac-dr, and displayed in GAIA using this toolbox.

More recently, Malcolm and Brad Cavanagh (of the JAC) have developed a recipe for spectro-polarimetry. After flat-fielding and sky-subtraction, the recipe extracts the dual-beam e and o spectra from the data taken at each waveplate angle. These data are processed with David Berry's polarimetry package POLPACK, before spectra in I, Q, U, P and TH are produced, the last two data products being displayed in a kapview window (see Figure 2).

With the flexibility offered by UFTI and UIST, combined with the development of these ORAC-DR recipes, the GAIA Polarimetry Toolbox and POLPACK, polarimetry has never been easier at UKIRT!

Finally, earlier this year Tim Gledhill of the University of Hertfordshire commissioned Circular Polarimetry with UIST. Circular polarimetry with UIST (and UFTI) is available to all UKIRT users. Proposals are welcomed. However, the quarterwave plate and additional hardware needed for circular polarimetry are owned by the University of Hertfordshire, so collaboration with U. Herts is requested.

Figure 2: Spectro-polarimetry in the IJ bands obtained with UIST and reduced with ORAC-DR.

Full details of linear imaging and spectro-polarimetry, circular polarimetry, and the software described above, are available from the UKIRT web pages: www.jach.hawaii.edu/UKIRT/instruments/irpol/irpol.html. Potential users are also welcome to contact Chris Davis at c.davis@jach.hawaii.edu.

View from the Top

Thor Wold

Another semester draws to a close, and now we come to "The WFCAM Semester" - 05b shall be the semester totally devoted to just one instrument for the first time in the history of UKIRT, as we strive to push forward with the UKIDSS surveys, particularly the UDS.

We three TSSs had enough fits trying to once again remember how to run the three cassegrain instruments after the 13 weeks of this last WFCAM shakedown period. It shall be most interesting when we have to encounter this once again - but this time after a continuous period of six months! We have banded together to create documentation to help us remember all the nuances, but please remember to bear with us a bit as we come out on the other side of this span of time.

Federal funding of $50 million for half of the realignment of Saddle Road has been passed by the US Congress in a new six-year Federal Highway Bill. This, in fact, is more than one-third of the total Federal spending allocated for the whole state of Hawai'i and is the largest project of them all in terms of money. This shows the determination to finally join the east and west sides of the island with a road that will better allow travel and commerce than the belt road.

In the meantime, the first section that bypasses the military base at Pohakuloa has been finished to grade and only now awaits paving. While there has not been any public discussion of how the new monies will be spent, if things continue according to the plans in place previously, this will mean that the road will be realigned on the east side first, so that travel from Hilo up to Hale Pohaku will be made even easier and safer.

The new Mauna Kea Education Center at the University Park is rapidly nearing completion and is still on schedule. The world-class planetarium ought to be fully completed by early next year, while the rest of the building and contents ought to be done by the end of this year. (They were nice enough to give me a certificate for four people to go to the planetarium in appreciation for my volunteering to participate in a video interactive display). The center just got a new director, someone who has had extensive experience with a tech museum in San Diego.

Up at your beloved Vacation Resort Hale Pohaku, things have been mercifully quiet the past several months. Some renovation for new offices for Subaru and Gemini are nearing completion. The work on replacing the siding on the outside of Building B has come to a halt, after the south wall was completed. Nothing has happened now since late last year. This is the most requested dorm building, so finding a way to get the work done without disturbing people's sleep is near impossible. MKSS is sort of waiting for a bit for a lull in the occupancy rate, but this is really unlikely anytime soon, so one wonders what they will end up doing. The logical idea might be to hire a contractor to hammer this out in a matter of days but this still does not seem to be the plan.

Other than this, nothing has changed of late (alas)...food and accommodations the same. While they appear to have gotten a few substantial pillows, we still have the not-quite-big-enough fitted sheets that still manage to pop loose. So far this summer, we have managed to avoid having any honeybee infestations. The HP Hot Flashes in the shower are still there but much more muted.

Now that we are into The WFCAM Semester, is it more unlikely we shall see as many of you as we usually do. That said, we do look forward to getting back to the cassegrain instruments in February and seeing more of our old friends coming back through again. In any case, hope to see you again soon!

Aloha!