201.8. SSSource table

201.10. SSSource table¶

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Last verified to run: 2025-06-20
Repository: github.com/lsst/tutorial-notebooks

Learning objective: To understand the contents of the SSSource table and how to access it.

LSST data products: SSSource

Packages: lsst.rsp, lsst.daf.butler

Credit: Originally developed by the Rubin Community Science team. Please consider acknowledging them if this notebook is used for the preparation of journal articles, software releases, or other notebooks.

Get Support: Everyone is encouraged to ask questions or raise issues in the Support Category of the Rubin Community Forum. Rubin staff will respond to all questions posted there.

1. Introduction¶

The SSSource table contains single-epoch solar system source information corresponding to a specific difference image detection.

• TAP table name: dp1.SSSource
• butler table name: ss_source
• columns: 23
• rows: 5,988

Related tutorials: The TAP and butler data access services are demonstrated in the 100-level "How to" tutorials.

1.1. Import packages¶

Import standard python packages numpy, matplotlib and astropy.

From the lsst package, import modules for the TAP service, the butler, and plotting.

In [1]:

import numpy as np
import matplotlib.pyplot as plt
from lsst.rsp import get_tap_service
from lsst.daf.butler import Butler
from lsst.utils.plotting import (get_multiband_plot_colors,
                                 get_multiband_plot_symbols)

1.2. Define parameters and functions¶

Create an instance of the TAP service, and assert that it exists.

In [2]:

service = get_tap_service("tap")
assert service is not None

Create an instance of the Rubin data butler, and assert that it exists.

In [3]:

butler = Butler('dp1', collections="LSSTComCam/DP1")
assert butler is not None

Define the colors and symbols to represent the LSST filters in plots.

In [4]:

filter_names = ['u', 'g', 'r', 'i', 'z', 'y']
filter_colors = get_multiband_plot_colors()
filter_symbols = get_multiband_plot_symbols()

2. Schema (columns)¶

To browse the table schema visit the Rubin schema browser, or use the TAP service via the Portal Aspect or as demonstrated in Section 2.1.

2.1. Retrieve table schema¶

To retrieve the table schema, define a query for the schema columns of the SSSource table and run the query job.

In [5]:

query = "SELECT column_name, datatype, description, unit " \
        "FROM tap_schema.columns " \
        "WHERE table_name = 'dp1.SSSource'"
job = service.submit_job(query)
job.run()
job.wait(phases=['COMPLETED', 'ERROR'])
print('Job phase is', job.phase)
if job.phase == 'ERROR':
    job.raise_if_error()

Job phase is COMPLETED

Retrieve the query results and display them as an astropy table with the to_table() attribute.

In [6]:

assert job.phase == 'COMPLETED'
results = job.fetch_result().to_table()
results

Out[6]:

Table length=23

column_name	datatype	description	unit
str64	str64	str512	str64
diaSourceId	long	Unique identifier of the observation
eclipticBeta	double	Ecliptic latitude	deg
eclipticLambda	double	Ecliptic longitude	deg
galacticB	double	Galactic latitute	deg
galacticL	double	Galactic longitude	deg
heliocentricDist	float	Heliocentric distance	AU
heliocentricVX	float	Cartesian heliocentric X velocity (at the emit time)	AU
heliocentricVY	float	Cartesian heliocentric Y velocity (at the emit time)	AU
heliocentricVZ	float	Cartesian heliocentric Z velocity (at the emit time)	AU
heliocentricX	float	Cartesian heliocentric X coordinate (at the emit time)	AU
heliocentricY	float	Cartesian heliocentric Y coordinate (at the emit time)	AU
heliocentricZ	float	Cartesian heliocentric Z coordinate (at the emit time)	AU
phaseAngle	float	Phase angle	deg
residualDec	double	Residual Dec vs. ephemeris	deg
residualRa	double	Residual R.A. vs. ephemeris	deg
ssObjectId	long	Unique identifier of the object.
topocentricDist	float	Topocentric distace	AU
topocentricVX	float	Cartesian topocentric X velocity (at the emit time)	AU
topocentricVY	float	Cartesian topocentric Y velocity (at the emit time)	AU
topocentricVZ	float	Cartesian topocentric Z velocity (at the emit time)	AU
topocentricX	float	Cartesian topocentric X coordinate (at the emit time)	AU
topocentricY	float	Cartesian topocentric Y coordinate (at the emit time)	AU
topocentricZ	float	Cartesian topocentric Z coordinate (at the emit time)	AU

The table displayed above has been truncated.

Option to print every column name as a list.

In [7]:

# for col in results['column_name']:
#     print(col)

Delete the job, but not the results.

In [8]:

del query
job.delete()

2.2. Key columns¶

Of the 23 columns of the SSSource table, several are the most commonly used.

2.2.1. Solar System object Id¶

The long integer that uniquely identifies each Solar System object.

• ssObjectId

2.2.2. Heliocentric distance¶

The cartesian heliocentric position and velocity coordinates:

• heliocentricX, heliocentricY, heliocentricZ, heliocentricVX, heliocentricVY, heliocentricVZ

The heliocentric distance:

• heliocentricDist

2.2.3. Topocentric distance¶

The topocentric position and velocity coordinates:

• topocentricX, topocentricY, topocentricZ, topocentricVX, topocentricVY, topocentricVZ

The topocentric distance:

• topocentricDist

2.2.4. Phase angle¶

The phase angle is the angle between the light incident onto an observed object and the light reflected from the object.

• phaseAngle

2.3. Descriptions and units¶

For a subset of the key columns show the table of their descriptions and units.

In [9]:

col_list = set(['ssObjectId', 'heliocentricDist', 'topocentricDist', 'phaseAngle'])
tx = [i for i, item in enumerate(results['column_name']) if item in col_list]
results[tx]

Out[9]:

Table length=4

column_name	datatype	description	unit
str64	str64	str512	str64
heliocentricDist	float	Heliocentric distance	AU
phaseAngle	float	Phase angle	deg
ssObjectId	long	Unique identifier of the object.
topocentricDist	float	Topocentric distace	AU

Clean up.

In [10]:

del col_list, tx, results

3. Data access¶

The SSSource table is available via the TAP service and the butler.

Recommended access method: TAP.

3.1. TAP (Table Access Protocol)¶

The SSSource table is stored in Qserv and accessible via the TAP services using ADQL queries.

3.1.1. Demo query¶

Define a query to return the four of the "key columns" from Section 2.3.

In [11]:

query = "SELECT ssObjectId, heliocentricDist, topocentricDist, phaseAngle "\
        "FROM dp1.SSSource " \
        "ORDER BY ssObjectId ASC "
job = service.submit_job(query)
job.run()
job.wait(phases=['COMPLETED', 'ERROR'])
print('Job phase is', job.phase)
if job.phase == 'ERROR':
    job.raise_if_error()

Job phase is COMPLETED

Fetch the results as an astropy table.

In [12]:

assert job.phase == 'COMPLETED'
results = job.fetch_result().to_table()
print(len(results))

5988

Option to display the table.

In [13]:

# results

Check if any visits had more than one source detected (with the option to print the results).

In [14]:

values, counts = np.unique(results['ssObjectId'], return_counts=True)
tx = np.where(counts > 1)[0]
print('Solar System objects with >1 detection: ', len(tx))
# for x in tx:
#    print('ssObjectId: ', values[x], '  number of sources', counts[x])

Solar System objects with >1 detection:  417

As an example, plot a histogram of the number of sources for each object.

In [15]:

fig, ax = plt.subplots(figsize=(4, 4))
ax.hist(counts[tx])
plt.xlabel('Number of sources per object')
plt.tight_layout()
plt.show()

Figure 1: Histogram of the number of source detections for every Solar System object with more than one detection.

Clean up.

In [16]:

job.delete()
del query, results, values, counts, tx

3.1.2. Joinable tables¶

The SSSource table can be joined to the DiaSource table on the column containing the unique visit identifier, ssObjectId.

The DiaSource table contains information about the astrometric and photometric measurements for solar system objects detected in difference images.

To the query used in Section 3.2.1, add a table join to the DiaSource table and retrieve columns midpointtMjdTai and band.

In [17]:

query = "SELECT sss.ssObjectId, sss.heliocentricDist, "\
        "sss.topocentricDist, sss.phaseAngle, "\
        "dia.midpointMjdTai, dia.band "\
        "FROM dp1.SSSource AS sss " \
        "JOIN dp1.DiaSource AS dia ON sss.ssObjectId = dia.ssObjectId " \
        "WHERE dia.ssObjectId > 0"
job = service.submit_job(query)
job.run()
job.wait(phases=['COMPLETED', 'ERROR'])
print('Job phase is', job.phase)
if job.phase == 'ERROR':
    job.raise_if_error()

Job phase is COMPLETED

Fetch the results as an astropy table.

In [18]:

assert job.phase == 'COMPLETED'
results = job.fetch_result().to_table()
print(len(results))

142640

Plot topocentric distance as a function of the observation midpoint of every Solar System source.

In [19]:

fig, ax = plt.subplots(figsize=(5, 5))
for filt in filter_names:
    fx = np.where(results['band'] == filt)[0]
    if len(fx) > 0:
        ax.plot(results['midpointMjdTai'][fx],
                results['topocentricDist'][fx],
                filter_symbols[filt], ms=5, mew=0, alpha=0.7,
                color=filter_colors[filt], label=filt)
plt.xlabel('midpointMjdTai')
plt.ylabel('topocentric distance (au)')
plt.legend(loc='upper left')
plt.show()

Figure 2: Topocentric distance as a function of the observation midpoint for every Solar System source, with colors and symbols to represent the five filters (ugriz) obtained on the nights of MJD = 60625 - 60658. The topocentric distance of all SSSources is not expected to be correlated with observation date, but rather this plot shows the 5 nights that the Low Ecliptic Latitude field were observed are obvious from the many more detections on those nights.

Clean up.

In [20]:

job.delete()
del query, results

3.2. Butler¶

TAP is the recommended way to access the solar system source table, but the butler can be used to retrieve the same table information.

Show that the ss_source table has no dimensions. For DP1, it can only be retrieved from the butler in full.

In [21]:

butler.get_dataset_type('ss_source')

Out[21]:

DatasetType('ss_source', {}, ArrowAstropy)

In [22]:

butler.get_dataset_type('ss_source').dimensions.required

Out[22]:

{}

3.2.1. Demo query¶

Define the columns to retrieve.

In [23]:

col_list = ['ssObjectId', 'heliocentricDist', 'topocentricDist', 'phaseAngle']

Get the data from the butler.

In [24]:

results = butler.get('ss_source', parameters={'columns': col_list})
print(len(results))

5988

Option to display the results.

In [25]:

# results

Plot phase angle as a function of heliocentric distance for every Solar System source.

In [26]:

fig, ax = plt.subplots(figsize=(4, 4))

ax.scatter(results['heliocentricDist'], results['phaseAngle'], s=0.5)

plt.xlabel('Heliocentric Distance (au)')
plt.ylabel('Phase angle (deg)')
plt.tight_layout()

plt.show()

Figure 3: Phase angle as a function of heliocentric distance for every Solar System source.

Clean up.

In [27]:

del col_list, results

In [ ]: