Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://star.arm.ac.uk/~ambn/iris.ps Äàòà èçìåíåíèÿ: Mon Nov 4 13:17:33 1996 Äàòà èíäåêñèðîâàíèÿ: Mon Oct 1 20:22:55 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 35

A&A manuscript no.
(will be inserted by hand later)
Your thesaurus codes are:
10 (07.13.2; 07.19.2; 07.13.1; 07.16.2: (7) Iris
ASTRONOMY
AND
ASTROPHYSICS
11.10.1996
(7) Iris: a possible source of Ordinary Chondrites?
F. Migliorini 1 , A. Manara 2 , A. Cellino 3 , M. Di Martino 3 , and V. Zappal`a 3
1 Armagh Observatory, College Hill, BT61 9DG, Armagh
pat@star.arm.ac.uk
2 Osservatorio Astronomico di Brera, via Brera, 28, 20121 Milano, Italy
manara@brera.mi.astro.it
3 Osservatorio Astronomico di Torino, strada Osservatorio, 20, 10025 Torino, Italy
cellino@to.astro.it ­ dimartino@to.astro.it ­ zappala@to.astro.it
Received ; accepted
Abstract. Rotationally resolved visible spectroscopy
(6000 ¸ 9500 š A) of (7) Iris is presented. Within a few
percents, no variation in Iris' visible spectrum over a ro­
tational period has been found. These data suggest that
the mineralogic properties of Iris' surface are globally ho­
mogeneous, although we cannot exclude the presence of
some texture and/or albedo variegation as suggested by
previous photometric and polarimetric studies available
in the literature. From a dynamical point of view, we es­
timate the ejection velocity required for collisional frag­
ments from this asteroid to be injected into the surround­
ing chaotic regions. The resulting velocity values are fairly
high, but not incompatible with the values suggested by
the present knowledge of catastrophic break­up phenom­
ena and by the observational constraints put by asteroid
families. Taking into account the close similarity between
Iris' spectrum and that of (6) Hebe, a typical S(IV)­type
object according with the most modern spectral classifi­
cations, we believe that (7) Iris may be a not negligible
source of Ordinary Chondrite meteorites.
Key words: asteroids -- meteorites -- spectroscopy -- (7)
Iris
1. Introduction
The origin of Ordinary Chondrites (hereinafter OCs) is an
important problem of modern planetary science. The two
main hypotheses, largely debated in recent years, are that
OCs either come from (at least some subset of) normal
S­type asteroids in the main belt, or from a hitherto un­
observed primordial population of small main­belt objects
(Q­types). The supporters of the first hypothesis, led by
Send offprint requests to: A. Manara
C.R. Chapman (Chapman 1996, Gaffey et al. 1989, Gaffey
et al. 1993) believe that the inconsistencies between the
spectral properties of OCs and S­type asteroids can be ex­
plained by a process of space weathering experienced by
S­type asteroids and strongly suggested by the results of
GALILEO observations of asteroids Ida and Gaspra. The
alternative hypothesis is mainly supported by J.F. Bell
(Bell 1986, Bell et al. 1989), and is based on the known
fact that S­type spectra do not match those of OCs.
Q­type asteroids provide a good spectral match of OCs
but, in the main belt, only (3628) BoŸznŸemcov'a has been
found (Binzel et al. 1993a) to be a good candidate (this
conclusion having been questioned by Chapman, 1996).
Other Q­types might be (1862) Apollo (McFadden et al.
1985, Bell & Keil 1988) and, very probably, 1993 VW (Di
Martino et al. 1995) and 1992 LR (Williams et al. 1994).
On the other hand, the rarity of these objects in the main
belt seems to indicate that they cannot explain the ob­
served abundance of OCs.
In recent years Gaffey et al. (1993) have pointed out
that a subsample of the S­type class, the S(IV) subclass
according to their classification, exhibit spectra that do
not exclude OC assemblages. They are considered to be
composed of an olivine­orthopiroxene (Ca­poor) surface
assemblage. Gaffey et al. (1993) analysed a set of 39 S­type
asteroids out of a sample of 144, classifying 11 of them as
belonging to the subset S(IV). It is notable that they are
concentrated near the 3:1 Kirkwood gap. Among the most
important objects belonging to the S(IV) subclass there
are the relatively large asteroids (6) Hebe and (7) Iris.
Farinella et al. (1993) estimated the relatively efficiency
of a large number of asteroids located close to either the
3:1 mean­motion resonance with Jupiter or the š 6 secu­
lar resonance with Saturn, as plausible meteorite sources.
Their analysis took into account both the closeness to the
resonances and the sizes of the objects, since these influ­
ence strongly the kind of collisional evolution and the pro­

2 F. Migliorini et al.: (7) Iris: a possible source of Ordinary Chondrites?
duced fluxes of collisional fragments. They concluded that
(6) Hebe should be a very efficient source of meteorites,
and due to its S(IV) classification it should be considered
as a possible major source of OCs. Also (7) Iris was found
to be among the objects characterised by a relatively high
delivery efficiency.
Following these arguments we have observed (7) Iris
through rotationally--resolved spectroscopy and have also
integrated its present orbit backward and forward, in or­
der to estimate the typical ejection velocities needed for
collisional fragments from this object to be injected into
the 3/1 resonance, taking into account also the dynamical
evolution of the parent body.
The paper is organised as follows: in Section 2 we re­
view the main properties of (7) Iris, while in Section 3
we address the problem of the delivery of fragments from
this asteroid to the 3/1 resonance. The results of our spec­
troscopic campaign are shown in Section 4, and the main
conclusions of this paper are discussed in Section 5.
2. (7) Iris: the current picture
(7) Iris is one of the biggest S­type asteroids in the main
belt (Tholen 1989, Tholen & Barucci 1989, Tedesco &
Veeder, 1992). It was first discovered by J.R. Hind in 1847
(Pilcher 1979). Its orbit (MPC 24084) was recently im­
proved by Wlodarczyr (1993) using 30 new astrometric
positions taken at the Observatory of Chorzow and 15
from three other observatories. The orbital elements are
listed in Table 1.
Since the 1950s, (7) Iris has been observed photoelec­
trically by several authors (Groeneveld & Kuiper 1954,
van Houten­Groeneveld & van Houten 1958, Taylor 1971,
Taylor 1977, Xing­Hai et al. 1982, Zhou et al. 1982, Zap­
pal`a & Di Martino, 1986). The rotation period has been
determined, and turns out to be 7.139 hours (Lagerkvist
et al. 1989).
In 1987 Lagerkvist & Williams first determined the
slope parameter (G) for (7) Iris, which turned out to be
0:262 \Sigma 0:011. The presently accepted value of H is 5.510
mag.
Iris was observed by the IRAS infrared satellite, lead­
ing to a determination of diameter and albedo. After a
recalibration of data, the diameter turns out to be about
200 km (199.83 km according to Tedesco & Veeder 1992)
with a oe error of about 10%; the visual albedo (p v ) is
0.2766\Sigma0.030.
In 1962 Gehrels & Owings first gave an estimate of the
orientation of the spin axis, and one year later Chang &
Chia­Shiang confirmed the previous measurements. An­
other, independent determination of the pole has been
given also by Zappal`a & Di Martino (1986). The most
recent pole determination is by Magnusson (1986), who
finds an ellipsoidal shape with a=b = 1:18 and b=c = 1:41
and a pole direction with ecliptic longitude and latitude
(–; fi) of either (15 \Sigma 5 ffi ; +25 \Sigma 15 ffi ) or (195 \Sigma 5 ffi ; +15 \Sigma 15 ffi ).
In 1990 Broglia & Manara carried out a polarimetric
study of (7) Iris. At a mean phase angle of 11.8 degrees,
Iris showed a mean polarization of P r = \Gamma0:0070 \Sigma 0:0002
with a relative polarization variation \DeltaP =P , where \DeltaP is
the total amplitude of the fitted curve, equal to 0:25 \Sigma 0:03.
The authors concluded that this remarkable variation im­
plied a variegate surface.
Also Hoffman & Geyer (1993) reported on variable
lightcurve irregularities in a short phase interval, and they
concluded that they could be explained by the presence of
a large albedo spot in the northern hemisphere of (7) Iris.
They also concluded that regions of different materials
should cover large but not uniformly distributed areas on
the surface.
Very recently, Mitchell et al. (1995) on the basis of
radar observations concluded that the surface roughness
is not negligible with respect to the asteroid's dimensions,
and this suggested the presence of either regional or scale­
dependent variations in small­scale structure.
Since the 1980s (7) Iris has been spectroscopically ob­
served. In 1982 Feierberg et al. published the first infrared
spectrum and after them Butterworth & Meadows (1985),
Green et al. 1985, Clark et al. 1992, Hiroi et al. 1993,
Roettger & Buratti 1994, Xu et al. 1995 and Gaffey &
Gilbert 1996 obtained spectroscopic data. However, none
of them performed rotationally--resolved spectroscopy.
3. Dynamics
We are interested in estimating the probability that frag­
ments from (7) Iris, produced by collisions with smaller
bodies, may be injected into the chaotic region associ­
ated with the 3:1 mean­motion resonance with Jupiter.
Of course, the probability of this kind of event depends
critically on the minimum velocity needed to reach the
resonance, and this is a function of the distance in the
phase space between Iris and the edges of the 3/1.
In principle, the conditions of closest approach be­
tween Iris and the 3/1 resonance could be derived by
computing the resonant proper elements of Iris. Resonant
proper elements have been used first by Morbidelli et al.
(1995) in order to determine the conditions of close ap­
proach between family members and edges of neighbour­
ing mean­motion resonances. These authors have shown
that, roughly speaking, each asteroid ``sees its own reso­
nances'' due to the interplay between oscillations of the as­
teroid orbital elements and pulsations of resonance edges.
Resonant proper elements are defined as the orbital ele­
ments of an asteroid in the conditions of closest approach
to a given resonance.
However, we are not interested here in deriving simply
the conditions of closest approach, but rather we want to
have an idea of the typical dynamical behaviour of Iris,
in order to check what is its typical range of semi­major
axis and eccentricity values, in order to evaluate the limits

F. Migliorini et al.: (7) Iris: a possible source of Ordinary Chondrites? 3
in the critical ejection velocity values required to inject
fragments into the 3/1 resonance at 2.5 AU.
Therefore we have integrated the orbit of Iris using a
RADAU15 integrator (Everhart 1985) for 1 million years
backwards and forwards on a Sun­SPARC workstation at
the Observatory of Milan. We used the orbital elements
supplied by Ephemerides of Minor Planet 1996 (see Table
1.). The data were stored every 500 years. We included all
the planets with the exception of Pluto and Mercury, the
mass of the latter being added to the Sun.
As could be expected due to the supposedly stable po­
sition of Iris in the main belt, the semimajor axis is very
stable (Fig. 1 lower left), whereas the inclination has a
variation of about 4 degrees (Fig. 1 upper left). The ec­
centricity ranges from 0.16 (present is 0.23) to 0.27 (Fig. 1
upper right). The values of perihelion and aphelion never
reach those of any planets on the timescale investigated
(Fig. 1 lower right). The integrations confirm that Iris is
in a stable orbit as could be expected also on the basis of
the proper elements quality codes given by Milani et al.
(1994).
The above results can be applied to derive the min­
imum ejection velocity that a fragment from Iris must
achieve in order to reach the border of the 3:1 mean mo­
tion resonance. As for a possible role played by the š 6
secular resonance, we decided to disregard it, since this
resonance is fairly distant from Iris in the phase space,
and at most 0.2% of fragments, according to Farinella et
al. 1993, could reach it.
A good approach to estimate the minimum ejection
velocity needed to reach the 3/1 for different values of the
eccentricity of Iris is to apply Gauss's formulae which give
the variations in orbital elements experienced by an orbit­
ing body suffering an abrupt velocity change (Brouwer &
Clemence 1961):
4a = 2
n(1 \Gamma e 2 ) 1=2
[(1 + e cos f)4v t + e sin f4v r )] (1)
4e = (1\Gammae 2 ) 1=2
na \Theta
h
e+2 cos f+e(cos f) 2
1+e cos f 4v t + sin f4v r
i (2)
4i = (1 \Gamma e 2 ) 1=2
na
cos(f + !)
1 + e cos(f) 4vw (3)
where n is the mean motion, while a, e and i are the
semi­major axis, eccentricity and inclination of the body,
respectively. f and ! are the true anomaly and the ar­
gument of perihelion of the body at the instant of the
velocity change. \Deltav r ; \Deltav t ; \Deltav w are the components of the
velocity change vector. For sake of simplicity, we will as­
sume a distribution of \Deltav with all the directions equally
likely, i.e. \Deltav r = \Deltav t = \Deltav w =j \Deltav j =
p
3. Taking into
account that:
n = 2ú
P
=
r
G(M fi +m ast: )
a 3
(4)
where P is the period of revolution, M fi and m ast are
respectively the mass of the Sun and the asteroid (the
latter being fully negligible, of course) we obtain from (1)
the following expression for the velocity value \Deltav needed
to give a variation \Deltaa in semi­major axis:
j \Deltav j=
r
G \Delta M fi
a 3 \Delta
\Deltaa
p
1 \Gamma e 2
2 \Delta
p
3
1 + e(cos f + sin f)
(5)
The first two terms of (5) are, once the parameters are
fixed, constants, while the latter term is a function of the
true anomaly of the parent at the instant of collision.
However, we should also take into account that the
above expression gives a velocity at infinity, whereas we
have to consider also the fact that the real fragments must
overcome also the gravitational field of the parent body.
In other words, the real ejection velocity is given by:
v ej =
p
v 2
esc + \Deltav 2 (6)
where v esc is the escape velocity from Iris. This can be
easily estimated on the basis of the nominal size of Iris
derived by IRAS: from the diameter value of 199.83 km
(Tedesco &Veeder 1992), and assuming an average density
of 2.5 g=cm 3 we obtain for v esc a value of about 120 m/sec
to be quadratically added to \Deltav.
The final result concerning the ejection velocity needed
to reach the 3/1 resonance is shown in Fig. 2 as a function
of true anomaly f and eccentricity of Iris.
In deriving the results shown in the above figure, the
adopted value of \Deltaa (see Eq. (5)) corresponds to the
closer edge of the 3/1 mean­motion resonance as given
by Farinella et al. (1993). The computation has been per­
formed taking into account also the V­shaped profile of
the resonance edge, when different possible values of Iris'
eccentricity are considered.
It is interesting to note that the range of variation is
quite big, within a factor of 2, depending on the position
along the orbit (f). Also the dependence on the eccentric­
ity is not negligible, for most values of f . The long­dashed
line corresponds to the highest value of the eccentricity
range of Iris, as found in the numerical integrations shown
above, while the solid line corresponds to the present ec­
centricity value and the short­dashed refers to the lowest
eccentricity limit.
The results indicate that the resulting velocities are
fairly high, but not totally unrealistic. Even assuming that
the maxima of the curves shown in Figure 2 are too high
to allow an injection of fragments into the 3/1, it is still
true that over a wide range of true anomalies (covering at
least one half of the orbit) the velocity values are still ac­
ceptable. In particular, we should note that the computed
velocity values have the meaning of average modules of ve­
locity for fragments ejected in an isotropic velocity field,
and refer to fragments having three equal velocity com­
ponents. In reality, the fragments actually injected into
the resonance should be those ejected mostly toward the

4 F. Migliorini et al.: (7) Iris: a possible source of Ordinary Chondrites?
resonance edges. These fragments, obviously do not have
three equal velocity components, and the module of veloc­
ity needed to reach the resonance edge is obviously lower.
As an example, if we consider fragments ejected exactly
along the v t direction (\Deltav r = \Deltav w = 0; \Deltav = \Deltav t ) and
we recompute the velocity value needed to reach the 3/1
border, we obtain the results shown in Fig. 2a. It is easy to
see that the resulting values are sensibly lower than in the
case shown in Fig. 2. As a consequence, the values shown
in Fig. 2 can be quite pessimistic, although it is better
to choose to be on the safe side in this kind of compu­
tations, since the relative fraction of fragments ejected in
favourable directions should not be very high in any case.
As a conclusion, we can say that over long timescales the
normal collisional history of an object like (7) Iris should
provide many events in which at least a small fraction (the
high­velocity end of the distribution, and/or the objects
injected in favourable directions) of collisional fragments
could reach the 3/1 resonance depending on the model as­
sumed from 1.2 and 3.8 % (Farinella et al. 1993), yielding
a fairly weak, but continuous contribution to the process
of injection of meteoritic material in the inner zone of the
solar system. It is known, in fact, that the 3/1 resonance
should be one of the major dynamical routes from the
asteroid main belt to the zone of terrestrial planets (Wis­
dom, 1983, 1985; Yoshikawa, 1990; Farinella et al. 1994).
As for other possible factors to be taken into account in
the computation of the minimumvelocity, any influence of
the rotation of the target on the escape velocity (Zappal`a
et al. 1984) is negligible in this case. For a sphere, the
equatorial velocity on the surface is:
v eq = 2úr
p
(7)
where r is Iris' radius and p is its rotational period. We
simply obtain about 22.6 m/sec which is negligible com­
pared to that required to reach 3:1 (of the order of 1
km/sec).
4. Observations
According to the modern understanding of the process
of collisional evolution of the asteroid belt, it is practi­
cally sure that during its lifetime an asteroid like (7) Iris
should have suffered energetic collisional events. Even in
the absence of a dynamical family associated with this
asteroid, some observational indication of the occurrence
of such events could come from the optical properties of
Iris' surface. In particular, as quoted in Section 2, some
evidence for albedo and/or surface texture heterogeneity
has been noticed by some authors. This could suggest the
presence of some large impact crater(s) on the surface of
Iris. The existence of a large crater could witness an ener­
getic event occurred in the past, which could be associated
with some episode of massive injection of fragments into
the 3/1 resonance. Moreover, the presence of a large crater
could produce observable spectroscopic variegation of the
surface, at least in the case of deeply excavated zones in
a differentiated body. In the case that such evidence of
differentiation could be achieved by spectroscopic means,
this could be interesting from the point of view of the kind
of meteorites that could originate from Iris. In particular,
it is known that OCs could hardly be reconciled with a
fully differentiated parent body
In order to test the mineralogical properties of (7) Iris
we obtained several reflectance spectra in visible wave­
lengths at different rotational phases. At the time of our
measurements the angle between the rotation axis and the
direction of the Earth (aspect angle) was about 120 ffi (or
60 ffi ) according to Magnusson's (1989) pole determination.
We are aware that near­infrared data would be more sen­
sitive to features more strongly diagnostic of particular
silicate assemblages. However even optical data are very
useful for deriving useful mineralogic information (Vilas
& McFadden 1992, Vilas et al. 1994).
Spectra were taken at Asiago--Ekar observatory using
a 1.82 m Cassegrain telescope equipped with a Boller &
Chivens Spectrograph and a CCD THOMSON TH7882
Thick UV--Coated 580 \Theta 388 pixels, each pixel having di­
mensions of 23¯m\Theta23¯m. The grating had 150 gr/mm
with a dispersion of 339 š A/mm in the first order. In ad­
dition to the spectra we have taken several biases, flat
fields, calibration lamps and several spectra of HD 191854
and 64 Hyades solar analogues (Hardorp 1978). They are
claimed to be indistinguishable from solar spectrum; in
particular the latter is one of the best known solar ana­
logues. The reduction technique was standard, using the
IRAF package. In Table 2. the circumstances of the ob­
servations are shown; the last column represents the ro­
tational phase (OE rot: based on a period of 7 h .139). Fig. 3
shows the averaged spectrum of (7) Iris compared to that
of (6) Hebe (Migliorini et al. 1996). Their similarity in the
visible region of wavelength is striking. The spectral range
is not exactly the same since the spectra were obtained us­
ing two different telescopes; however, the spectral trends
are closely similar. The data from 8­color survey (Tholen
1984) are superimposed on the average spectrum of Iris,
the agreement is very sharp. Moreover we have checked
our optical spectrum with the one kindly provided by the
SMASS survey (Xu et al. 1995) and differences are within
few percent. In Fig. 4 we can see Iris' spectra correspond­
ing to different rotational phases. In order to emphasise
variations among the spectra, taken at different rotational
phases, we plotted in Fig. 5 the ratio between each spec­
trum of Fig. 4 with the averaged one of Fig. 3. No strong
differences are visible, apart from fluctuations of the red
part due to the low sensibility of CCD and also to telluric
absorption band centered at about 9200 š A. On the whole,
our observations do not indicate the presence of spectral
variations related to surface heterogeneity.

F. Migliorini et al.: (7) Iris: a possible source of Ordinary Chondrites? 5
5. Conclusions
The fairly high values of the ejection velocity required to
inject fragments from Iris into the 3/1 resonance (Section
2), could suggest that this object should not considered
as a major source of meteoritic material. Nevertheless as
quoted in Section 2 some kind of heterogeneity seems likely
to exist on the basis of the results of observations based
on different techniques (photometry, polarimetry, radar)
suggesting that some energetic impacts happened; how­
ever from spectroscopy we have not any further proof of
the occurrence of energetic impact events occurred in the
past. The lack of any spectroscopic evidence of surface het­
erogeneity resulting from our observations should not be
overemphasised.
However, it has been shown by observations of Vesta
family and its surrounding objects (Binzel & Xu, 1993a)
that very high ejection velocities (of the order of 1 km/sec)
of fragments can occur in collisional events involving large
asteroids. This is also confirmed by typical values of ejec­
tion velocities that can be derived from an analysis of the
other families presently known (Zappal`a et al., 1996). On
the basis of these evidences we should be cautious in rul­
ing out a possible role of objects like (7) Iris as important
source of meteorites. In particular, we should take into ac­
count that the size of Iris is favourable for a high­delivery
efficiency (Farinella et al. 1993).
So the main conclusions of this paper can be sum­
marised as follows:
i. from a dynamical point of view (7) Iris is a possible
source of debris through the 3:1 mean motion reso­
nance with Jupiter. The required ejection velocity has
been shown to be not implausible, although fairly high.
ii. Spectroscopically Iris is a typical S(IV)­type asteroid.
This makes this object a good candidate for being a
supplier of OCs (Gaffey et al. 1993). No rotationally­
related spectral features have been found, but this does
not rule out the possibility that a real surface texture
heterogeneity, possibly related to the presence of large
impact craters, could actually exist. Rather, the lack
of spectroscopically observable features on the surface,
does not support the idea that Iris could be a differ­
entiated object. In turn, this fact could strengthen the
conjecture that this object could be a supplier of OCs.
Acknowledgements.
The research was supported by the EU­HCM programme, con­
tract number CHRX--CT94--0445; A. Manara, A. Cellino, M.
Di Martino and V. Zappal`a were also partially supported by
grant ASI--94--RS--69 of Italian Space Agency (ASI). The au­
thors would like to thank also M.E. Bailey, P. Farinella and
A. Morbidelli for useful discussions and suggestions and Bill
Napier for improving the english.
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Fig. 1: orbital parameters of (7) Iris. In the upper left
corner the inclination versus the longitude of ascending
node is shown. In the upper right eccentricity is shown
whereas in the lower left the semimajor axis is plotted.
The lower right corn er shows the value of Iris' perihelion
and aphelion versus the epoch, dashed­line is at the posi­
tion of Mars' orbit.
Fig. 2: required velocity to reach 3:1 resonance versus
true anomaly (f) is shown. Solid line is referred to the
current value of eccentricity, whereas short­dashed line is
for the minimum value and the long­dashed line is for the
highest.
Fig. 2a: required velocity to reach 3:1 resonance versus
true anomaly (f) in the case of \Deltav w = \Deltav r = 0 and
\Deltav t = \Deltav. Solid line is referred to the current value of ec­
centricity, whereas short­dashed line is for the minimum
value and the long­dashed line is for the highest.
Fig. 3: averaged reflectance spectrum of (7) Iris compared
with (6) Hebe (Migliorini et al. 1996). On the spectrum
of Iris is superimposed the 8­color survey (Tholen 1984).
Fig. 4: rotationally resolved spectra of (7) Iris. Data are
vertically offset for clarity.
Fig. 5: ratio between the averaged spectrum of (7) Iris
(Fig. 3) and the spectra taken at different rotational
phases (Fig. 4). All the spectra are flat to within few per­
cent; some difference are found in the red part (? 9000 š A)
due to telluric water absorptions and the relatively low­
efficiency of CCD.
This article was processed by the author using Springer­Verlag
L A T E X A&A style file L­AA version 3.

F. Migliorini et al.: (7) Iris: a possible source of Ordinary Chondrites? 7
Table 1. ORBITAL ELEMENTS OF (7) IRIS
a e i !
\Omega M JD
2.3856068 0.2303295 5 ffi .52310 145 ffi .25704 259 ffi .92548 106 ffi .98343 2450400.5
Table 2. Observational Circumstances
Date UT ff ffi Airmass OE rot:
apparent apparent
16/10/95 22 h 02 m 04 h 42 m 14 s .6 +27 ffi 28' 1.647 0.000
16/10/95 22 h 57 m 04 h 42 m 15 s .4 +27 ffi 28' 1.369 0.128
16/10/95 23 h 45 m 04 h 42 m 16 s .0 +27 ffi 28' 1.220 0.240
17/10/95 00 h 10 m 04 h 42 m 16 s .3 +27 ffi 28' 1.165 0.298
17/10/95 00 h 38 m 04 h 42 m 16 s .7 +27 ffi 28' 1.119 0.364
17/10/95 01 h 46 m 04 h 42 m 17 s .5 +27 ffi 27' 1.060 0.522 ?
17/10/95 02 h 08 m 04 h 42 m 17 s .8 +27 ffi 27' 1.054 0.570
17/10/95 03 h 06 m 04 h 42 m 18 s .5 +27 ffi 27' 1.071 0.710
17/10/95 22 h 12 m 04 h 42 m 34 s .0 +27 ffi 27' 1.060 0.387
17/10/95 23 h 20 m 04 h 42 m 34 s .9 +27 ffi 26' 1.564 0.544
18/10/95 00 h 33 m 04 h 42 m 35 s .6 +27 ffi 26' 1.278 0.714
18/10/95 00 h 46 m 04 h 42 m 35 s .8 +27 ffi 26' 1.121 0.745
18/10/95 01 h 39 m 04 h 42 m 36 s .3 +27 ffi 26' 1.104 0.868
18/10/95 02 h 15 m 04 h 42 m 36 s .7 +27 ffi 26' 1.054 0.952
18/10/95 03 h 04 m 04 h 42 m 37 s .3 +27 ffi 26' 1.072 0.067 ?
18/10/95 22 h 10 m 04 h 42 m 50 s .8 +27 ffi 25' 1.555 0.742
18/10/95 23 h 15 m 04 h 42 m 51 s .4 +27 ffi 25' 1.282 0.894
19/10/95 00 h 27 m 04 h 42 m 52 s .0 +27 ffi 25' 1.125 0.062
19/10/95 01 h 13 m 04 h 42 m 52 s .4 +27 ffi 25' 1.074 0.169
19/10/95 02 h 00 m 04 h 42 m 52 s .8 +27 ffi 24' 1.054 0.279
? bad frames, not used