Stellar occultations

Triton, November 29, 2003

Titan, November 14, 2003

On 2003 November 14 6:57 UT, Titan will occult TYC 1343-1865-1, a V=10.4 magnitude star. This event is described by Bruno Sicardy, who credits Claudio Martinez (Argentina) for the identification. This event is 2.8 mags brighter in K than the 2001 Dec 20 event, making the star brighter than unresolved Titan in K. There is another, brighter, Titan occultation on November 14, 2003, visible from South Africa. See Bruno's site for details.

summary

DATE & TIME = 2003 November 14 6:57 UT (UT)
RA and Dec (J2000) = 06 55 17.77 +22 06 01.2 (USNO 2.0).
V = 10.4 (Hipparchos and Tycho catalogs)

fluxes

From  2MASS  Catalog (star name 0655177+220601)                
   RAJ2000     DEJ2000       Jmag   e_Jmag    Hmag   e_Hmag    Kmag   e_Kmag
   "h:m:s"      "d:m:s"      deg     deg       mag     mag      mag      mag
 06 55 17.75 +22 06 01.2    8.569   0.035    8.060   0.035    7.898    0.034

Titan magnitudes ( Astrophysical Quantities, 4th Edition ) 
for unresolved measurements of Titan.
        V        J         H          K        L
      8.04      7.84      8.15      8.53     10.23

Estimated star-Titan magnitude differences

        V        J         H          K        L
       2.3      0.7      -0.1        -0.6     -2.4

This can be seen graphically in a JPG plot of Titan and stellar flux.

plans

July 8, 2003: Plans are in flux. Check back here in a few weeks. Send mail to Leslie Young (layoung@boulder.swri.edu) and Bruno Sicardy (bruno.sicardy@obspm.fr) if you're interested in either 2003 Nov 14 Titan event.

Saturn, December 24 2002

Saturn, November 15 2002

Pluto, July 20 2002

Titan, December 20 2001

On December 20, 2001, Titan will occult a 12.4 magnitude star. The central chord passes over the southwestern United States, and the central flash should be observable from several major observatories. The circumstances of the event is very favorable for North America, occuring near Titan opposition, with Titan at low airmasses.

summary

Star=NV0435215+200905
DATE & TIME = 2001 December 20 5:20 (UT)
RA and Dec (J2000) = 04:35:21.5212 +20:09:05.288 (Ron Stone).
Errors in the position = 0.043 arcsec (ra) and 0.034 arcsec (dec)
R magnitude = 12.4
miss distance = 0.3 (arcsec)
velocity = 19.3 km/s
source = Amanda Bosh, Ron Stone

visibility

Here is the Earth, as seen by Titan. The sub-Titan point is the center of the disk, and the sun is more than 12 degrees below the horizen for areas that are dark. The occultation will be visible from most of the Americas, in particular from the Western U. S.

Tracks of the path of the star behind Titan from several observatories. The smaller inner circle has a radius of 100 km, and approximately shows the location where the central flach may be visible.
Tracks of individual observatories:
U Ariz. Obs., Catalina Station
Lick Observatory
McDonald Observatory
Kitt Peak National Observatory
Lowell Observatory
Palomar Observatory
WIRO
Mount Lemmon
Mauna Kea
Mount Wilson
A postscript file showing the position of Saturn and its satellites at 2001 Dec 20 5:20 UT , generated from the PDS ring node planet viewers site

fluxes

From  2MASS  Catalog (star name  0435215+200905)                
   RAJ2000     DEJ2000       Jmag   e_Jmag    Hmag   e_Hmag    Kmag   e_Kmag
   "h:m:s"      "d:m:s"      deg     deg       mag     mag      mag      mag
 04 35 21.52  +20 09 05.3   11.447   0.033   10.739   0.034   10.612   0.031 

According to the 2MASS survey, the star has J-K = 0.83
Using Zombeck's Handbook of Astromony & Astrophysics, we estimate that the
star is stellar type K9V or K4III, with L = 10.4 and V = 13.8.

From the  USNO-A2.0  Catalogue (via Vizier)                          
     RAJ2000      DEJ2000       USNO-A2.0     Bmag  Rmag   
     "h:m:s"       "d:m:s"                      mag   mag   
   04 35 21.541  +20 09 05.25  1050-01322686   14.5  12.4

Titan magnitudes ( Astrophysical Quantities, 4th Edition ) 
for unresolved measurements of Titan.
        V        J         H          K        L
      8.04      7.84      8.15      8.53     10.23

What does this mean for observing strategy? The contrast inproves at we go farther into the IR, both because the star is redder than the sun, and because of Titan's impressive methane absorption.

Estimated star-Titan magnitude differences

        V        J         H          K        L
       5.8      3.6       2.6        2.1      0.1

This can be seen graphically in a Postscript or GIF plot of Titan and stellar flux. The fluxes are also available in tabular form, with accompaning documentation, and an ASCII table .
How about the worry that the methane absorption is strong enoung in the L band to degrade the central flash? At the strongest absorption, the tau=1 altitude is 178 km -- probably fine. The tau=1 altitudes and pressures are found here .

timing

Effective stellar diameter = 0.2 to 0.3 km = 10 to 20 msec
Fresnel scale [sqrt(wavelength*dist)]= 1 km (52 msec) at 0.89 micron, 1.6 km (83 msec) at 2.2 micron.
Scale height is about 50 km, or about 2.6 sec/scale height.
A one-second duty cycle will give a vertical resolution comprable to that achieved by 28 Sgr. Faster is better if the SNR can stand it, but try to keep the deadtime to less than 10%.
For your predicted midtime, see the minite ticks in the individual visiblility plots. The flux should start to drop about 3 minutes prior to your predicted midtime. Get a good baseline before and after -- at least ten minutes, prerferably half an hour. This is especially important in Hawaii, where Titan is relatively low (38 deg altitude) at midtime, and we need to establish the extintion.
Accurate timing is essential. Resources include the Network Timing Protocol (NTP) . Also recall that cp -p and scp -p preserve file modification times.

plans

Observers and other interested parties: Antonin Bouchez (antonin@gps.caltech.edu), Tom Bida (tbida@lowell.edu), Mike Brown (mbrown@gps.caltech.edu), Imke de Pater (imke@floris.Berkeley.EDU), Ted Dunham (dunham@lowell.edu), Jim Elliot (jle@mit.edu). Bob Howell (rhowell@uwyo.edu), Bruce Macintosh (bmac@igpp.ucllnl.org), Phil Massey (massey@lowell.edu), Dave Osip (osip@MIT.EDU), Henry Roe (hroe@floris.Berkeley.EDU), Scott Severson (severson@ucolick.org), Brian Taylor (taylor@lowell.edu), Joanna Thomas-Osip (jet@MIT.EDU), Bob West (raw@west.jpl.nasa.gov), Eliot Young (efy@boulder.swri.edu), Leslie Young (layoung@boulder.swri.edu) Send mail to all observers

                                                                Event times   
Location     Observers              Instrument  Dates      Start     Mid     End   Track loc.
--------     ---------              ----------  --------- ------- ------- -------  -----
WIRO         Howell                 IOCAM       Dec 18,19 5:19:16 5:22:00 5:24:45  698 N
Lick Shane   Severson/LYoung        IRCAL+AO    Dec 18,19 5:20:24 5:23:12 5:25:59  389 N
Lowell 72"   Dunham/Bida/Taylor     IRCAM       Dec 19    5:19:41 5:22:29 5:25:16   79 N
Palomar 200" Brown/Bouchez/West     PHARO       Dec 19    5:20:07 5:22:55 5:25:43   76 S
AEOS         EYoung                 AEOS        Dec 12,19 5:23:08 5:25:53 5:28:00  721 S
Keck II      de Pater/Roe/McIntosh  NIRSPEC/AO  Dec 17,19 5:23:08 5:25:52 5:28:00  836 S
IRTF         Osip/Thomas-Osip       SpeX        Dec 18,19 5:23:08 5:25:52 5:28:00  836 S

Times are for the Ra and dec provided by Ron Stone. Start and end times are for a radius of 3239 km, when the flux should be at 99% of the unocculted flux (i.e., the start of the drop). It is recommended that observers take data continuously for an hour surrounding closest approach.
The error in timing due to Ron's error in the star position is ~13 seconds.
The uncertainty in Titan's atmosphere alters the midtimes by about 20 seconds and the 99% flux level by about 4 seconds. This is based on the difference in timing caclulated from the twi extreme models in Yelle, Strobel, Lellouch, and Gautier 1994, "Engineering models forTitan's atmosphere." Detailed plans and scientific motivation: Lick/Shane (IR, AO, possiple central flash) Haleakula (visible, AO)

status

Once an AO system was turned on the star, we got the wonderful news that the star was in fact a binary:

Wed, 19 Dec 2001 20:11:04 -0800 (PST)

Everyone,

        Myself, Mike Brown, and Bob West have been imaging with AO from
the Palomar 200" for ~30 minutes now and the target star is a clearly
seperated binary.  Separation is 1.5", PA ~96 degrees.  So for most
observers, both components will be occulted.  Good luck everyone.

Antonin Bouchez

This doubles the number of chords across Titan.
Below are excerpts from observer's reports immediately following the event. (Observer's first impressions about the SNR have not been included, since that can change greatly during reduction).

Location     Post-event observer's reports
--------     -----------------------------
WIRO         Observed at 2.38 um.  Conditions looked good although we had some
             clouds a little earlier in the evening.

Lick Shane   Unable to open at Lick due to high humidity, 
             high winds, thick clouds, and occasional drizzle.

Lowell 72"   We got a lot of data here at Lowell.

Palomar 200" Observations from Palomar went perfectly. Star 1 hit just 
             above the equator and we could watch it travel along the limb 
             all the way to the north pole and back down and finally out. 
             Star 2 did the same thing to the south a few minutes later. 
             Looks like we were likely on the centerline of the centroid, 
             but just missed being on the center of either of the two stars.

AEOS         observations were successful at 
             Haleakula, at visible wavelengths (0.75-1.0 micron).

Keck II      At Keck we were hindered by large overhead for writing to
             disk, so had to go with longer exposures and watch the star(s!)
             trail in each long image.  (Due to hardware there's an approx.
             8sec overhead to every image that's written out separately.)

IRTF         We got the event from the IRTF, although seeing was 1.5".

Status links:
Palomar web page with some images and MPEG movies of the occultation imaging experiment.

thanks

Thanks to Mark Lemmon for Titan albedos; Roger Yelle, Emmanuel Lellouch, and Darrell Strobel for Titan models.

Triton, November 04 1997

On November 4, 1997, Triton will occult a 10.5 magnitude star (C. Olkin, PhD thesis, 1996, p. 163). Details of the of the occultation prediction is Cathy's prediction page.

Jupiter, November 13 1997

On November 13, 1997, Jupiter will occult a 6.6 magnitude star. This happens during Jupiter's ring-plane crossing, but unfortunately the path of the star doesn't cross the rings.

summary

Star=ppm238409=HD 201057 = BD-18 5862=SAO 164156=HR 8083
DATE & TIME = 1997/11/13 02:36:15 (UT)
RA and Dec (J2000) = 21:07:44.641 -17:27:21.27 (from PPM catalog)
V magnitude = 6.03 (from HD catalog)
miss distance = 15.60 (arcsec)
velocity = 16.6 km/s
source = Doug Mink

visibility

Here is the Earth, as seen by Jupiter. The sub-Jupiter point is the center of the disk, and the sun is more than 12 degrees below the horizen for areas that are dark. The occultation will be visible from most of the Americas, in particular from the Western U. S.

Here are three views of the path of the star behind Jupiter.
1 The path of the star, as seen from Kitt Peak (generated by Doug Mink).
2 The path of the star, as seen from Lick Observatory (generated by Doug Mink).
3 The path of the star, as seen from Lowell Observatory, showing the ring geometry (generated by Amanda Bosh).

fluxes

Often, for stellar occultations by giant planets, we choose to observe in the near infrared, at wavelengths where methane absorbs, to cut down on the flux from the planet. In this case, the star is quite blue, with a spectral type of A0, and an alternate strategy is to observe at 380-450 nm.

You can compare the fluxes in the blue (300-600 nm), near IR (1000-2474 nm), or the whole range . Also it is in an ascii table . In all three plots, the flux from the occulted star is plotted as a dotted line, and the average flux per square arcsec from Jupiter is plotted as a solid line.

The flux from HR 8083 is scaled from the flux from Vega, using the HD magnitude of 6.0 for HR 8083. The flux from Vega shortward of 1050 nm was downloaded from ESO's spectral standard page . Longward of 1050 nm, I used the Rayleigh-Jeans Law, using the fluxes for a zero magnitude star to scale the flux.

The geometric albedos of Jupiter were downloaded from Nancy Chanover's Jupiter reflectivity page. I used Erich Karkoschka's full-disk albedos in the visible (Karkoschka, E. 1994. Spectrophotometry of the Jovian planets and Titan at 300- to 1000-nm wavelength: the methane spectrum. Icarus 111, 174), and Clark and McCord's disk-centered I/F in the infrared (Clark, R. N. and T. B. McCord 1979. Jupiter and Saturn: Near-infrared spectral albedos. Icarus 40, 180). I divided the Clark & McCord spectrum by 3/2 (q for a Lambert sphere), to bring their fluxes in line with the Karkoscka.

The solar spectrum was provided by Bob Kurucz.

Triton, July 18 1997

On July 18, 1997, Triton occulted a 12th magnitude star. Here is the account I sent Roger Yelle, describing our attempt to observe this event, which I've posted here just for grins.

Last updated 14 Oct 1997 by Leslie Young, layoung@bu.edu , http://deepthought.bu.edu/~layoung