for astronomers

The INO340 Telescope

Overview:

The INO340 is a 3.4-m Ritchey–Chrétien Cassegrain telescope operated by the Iranian National Observatory. Its primary mirror is made of ceramic ZERODUR®, with an optical diameter of 3300 mm, a thickness of 180 mm ± 10 mm, and a mass of ~4000 kg. The mirror has a focal ratio of f/1.49, a central hole of 700 mm, and a surface roughness of <2 nm RMS. The secondary mirror, also made of ZERODUR®, is convex with an optical diameter of 582.4 mm, a thickness of 90 mm at the center, and a mass of ~60 kg. The Cassegrain focus provides a final focal ratio of f/11.24. The telescope optical design delivers an unvignetted field of view of up to 20 arcminutes, while the currently installed KEPLER KL4040 camera provides a usable imaging field of 3×3 arcminutes, which can be increased to 6.6 × 6.6 arcminutes using a focal reducer. Three bent Cassegrain ports are available, each with a field of view of 8 arcminutes. All foci are equipped with instrument rotators and autoguiders, and acquisition cameras are available for field verification. The telescope operates over a wavelength range of 325–2500 nm, with an entrance pupil located on the primary and a back focal distance of 1670 mm. The telescope is mounted on an altitude–azimuth structure and is normally operated by staff: observers submit proposals, and the INO observing team conducts the observations and provides the data for download. Occasional on-site observing may be arranged under special circumstances, with visitors accompanied by the observing team.

The Optics The Mounting Instruments Object Visibility Checker Signal To Noise Calculator Applying for Telescope Time

The optical system of the INO340 is a Ritchey–Chrétien Cassegrain with a hyperboloidal primary and a convex hyperboloidal secondary mirror, optimized to deliver high image quality over a wide field of view. The primary mirror has a diameter of 3.4 m and a focal ratio of f/1.49, giving a final system focal ratio of f/11.24 at the Cassegrain focus. The entrance pupil is located on the primary mirror, and the system provides a back focal distance of 1670 mm.

The telescope operates over a wavelength range from 325 nm to 2500 nm, enabling observations from the near-ultraviolet to the near-infrared. At the main Cassegrain focus, the optical design provides an unvignetted field of view of 20 arc min, well corrected for off-axis aberrations. In addition to the main focus, three bent foci are provided, each offering a field of view of 8 arc min, allowing flexible instrument mounting and operation.

The mirrors are fabricated from ZERODUR®️ ceramic, providing excellent thermal and mechanical stability due to its negligible coefficient of thermal expansion. The optical surfaces are polished to a micro-roughness below 2 nm RMS, ensuring high throughput and image quality across the full spectral range. Active support and positioning systems are employed to maintain the mirror figures and alignment during telescope operation, compensating for gravitational and thermal deformations.

The scale at the Cassegrain focus is 0.18526 mm per arc sec, corresponding to a plate scale well matched to modern imaging and spectroscopic instrumentation. The optical design of INO340 delivers a compact, high-performance system, combining wide-field capability, broad wavelength coverage, and excellent image quality for a wide range of astronomical applications.

Optical characteristics of INO340 foci

	Cassegrain Focus
Focal length (mm)	~ 38212
Focal ratio	f/11.24
Unvignetted Field diameter (arcmin)	20
Scale (arcsec/mm)	5.398

Spot diagram for a flat focal surface at the nominal cassegrain focus of the INO340 telescope showing images produced on axis and at 3, 4.5 and 6 Arcminutes (units are µm).

On axis image images produced at the cassegrain focus of the INO340 telescope when focus is moved from the nominal position by the amounts shown on top of each image (units are µm).

The INO340 telescope is mounted on an altitude–azimuth and is controlled by the INOCS system, which drives the main hour-angle and declination axes, the Cassegrain instrument rotator, the focus, and the dome. The observer interacts with the telescope via a dedicated software interface from the control room, which allows entering target properties, pointing, exposure times, and filter selection, then starting the observation automatically. Adjustments to telescope tracking can be made automatically by the telescope control system.

The INO340 operational range is:

Zenith distance < 68°
– 6 h < hour angle < + 6 h
Declination > -30°

Pointing accuracy is 3 arcseconds. Tracking precision (assisted) of 0.2 arcseconds over a 10-minute interval. Blind offsets are typically accurate to 3 arcseconds.

The INO340 telescope is equipped with a KEPLER KL4040 FLI scientific CCD camera at the main Cassegrain focus, delivering high sensitivity optical imaging across a 3.3′ unvignetted field of view. The KL4040 can also be equipped with a focal reducer at the Cassegrain focus, which provides a wider 6.6′×6.6′ field of view for imaging larger sky areas.

This camera offers three gain modes: High (sensitive to faint details, gain ~0.5–2.5 e⁻/ADU), Low (handles bright regions, gain ~4.5–35.7 e⁻/ADU), and Merge (combined High + Low for wide dynamic range).

The KL4040 FI is a front-illuminated, cooled sCMOS camera with 4096 × 4096 pixels, 9 × 9 μm pixel size, and a 36.9 × 36.9 mm imaging area (diagonal 52.1 mm). It provides high quantum efficiency (~74% peak QE), low read noise (~3.7 e⁻ high gain), a dynamic range of 85.2 dB (HDR), and full well capacity of 70,000 e⁻. The camera supports a maximum frame rate of 23 fps (QSFP interface optional) and features rolling shutter readout, with high-speed HDR mode producing 12-bit linear images. Dark current is approximately 0.08 eps at -10C, which is the chosen temperature for standard operations of the telescope.

CCD Parameters

Pixel Size (μm)	9×9
Resolution (pixels)	4096 × 4096
Imaging Area (mm)	36.9 × 36.9
Electrons per ADU	0.95 – 1.05
Saturation (e-)	70000
Peak QE	74%
Read Noise (High gain)	3.7 e-
Dark Current @ -20C	0.08 eps at -10C

Filters for CCD Imaging on INO340

The INO340 telescope offers two high-quality filter systems: the Sloan (SDSS) u′g′r′i′ set and the Kron–Cousins (KC) UBVRI set. These systems provide astronomers with flexible options for broadband photometry, supporting both modern SDSS-based calibration and traditional UBVRI stellar classification.

The Sloan filters cover ultraviolet through optical wavelengths with sharply defined passbands that enable effective photometry and high signal-to-noise ratios for a wide range of targets. Observations using these filters are tied to the SDSS standard-star network, allowing high-precision absolute photometry in the AB magnitude system.

The Kron–Cousins UBVRI filters are specifically optimized for Silicon CCD detectors. They isolate critical spectral bands for stellar measurements while minimizing focus changes between filters. Each filter is manufactured with high optical quality and excellent out-of-band blocking to ensure accurate and repeatable photometry.

Filter Set	Filter	Central Wavelength (nm)	Bandwidth (nm)	Peak Transmission
SDSS u′g′r′i′	u′	354	57	> 70 %
	g′	477	139	> 80 %
	r′	623	137	> 85 %
	i′	762	153	> 85 %
KC UBVRI	U	365	60	> 50 %
	B	440	100	> 70 %
	V	520	90	> 70 %
	R	760	250	> 70 %
	I	800	150	> 70 %

In addition to the above, the development of a dedicated spectrograph is presently underway, with implementation planned as part of the next stage of the INO340 instrumentation program.

At present, the STARALT tool is provided as a recommended resource for INO astronomers to assess target visibility and plan observations.

The tool enables users to evaluate the visibility of astronomical targets from a selected observatory site by producing altitude–time plots over a given night. This allows the identification of optimal observing windows, taking into account constraints such as airmass limits and twilight conditions.

To use STARALT, users input the target name or celestial coordinates (RA/Dec), select the desired observing date, and choose the observatory location. The resulting output provides a clear graphical representation of target elevation throughout the night.

For INO-based planning, the Iranian National Observatory location can be selected directly from the Observatory dropdown menu within the STARALT interface, ensuring accurate site-specific visibility calculations for the INO340 telescope.

https://astro.ing.iac.es/staralt/

The INO340 SNR Calculator is a Python-based tool designed to estimate the expected signal-to-noise ratio for astronomical observations with the INO340 telescope. The pipeline combines instrumental parameters, site conditions, and astrophysical models to provide a physically consistent SNR estimation for a given target and exposure time.

The calculation incorporates atmospheric extinction, airmass effects, sky background contribution (including Moon illumination and separation), detector characteristics (read noise, gain, dark current), filter transmission properties, and telescope collecting area. Sky brightness is estimated dynamically using a calibrated sky model, while target flux is derived from standard photometric conversions. The final SNR is computed from the total signal and combined noise contributions within the photometric aperture.

The SNR Calculator is provided as a Python-based tool intended for local execution. Once set up, it can be run to access the graphical interface for input and calculation.

Users are guided through a structured input sequence, including:

Target coordinates (RA, Dec)
Observation date and time (local Tehran time)
Object magnitude and selected filter
Seeing conditions and detector binning

After entering the required parameters and selecting an exposure time, the tool performs a complete signal-to-noise calculation using the INO340 instrument and site model, and returns the final SNR estimate for the specified configuration. You can download the calculator by clicking the button below.

INO SNR Calculator

Researchers wishing to use the INO340 must submit a scientific proposal during an official call for proposals. Time is allocated on the basis of scientific merit, technical feasibility, and the suitability of the program for the telescope and its instrumentation.

Time Allocation

Observing time on the INO340 is awarded by the INO340 Time Allocation Committee (TAC) following a national call for proposals. The telescope operates in three-month observing semesters and all observations are conducted in service (queue) mode by the INO observing team.

Calls for proposals are issued periodically for observing time. At present, project activities are temporarily suspended until further notice. Updates regarding future calls will be announced in due course. Interested applicants are encouraged to revisit this website for announcements at a later time. For general enquiries, please contact: ino@ipm.ir.

Proposals are accepted from researchers affiliated with Iranian institutions, and exact deadlines for subsequent semesters will be announced with each call.

Observing Mode

All regular programs on the INO340 are conducted in service (queue) mode and executed by INO staff astronomers under suitable observing conditions. Programs are selected from the queue according to their scientific ranking and the prevailing conditions, including seeing, sky transparency, target visibility, airmass constraints, and instrument availability. This approach ensures efficient use of telescope time and maximizes scientific return.

Once observations are completed, the data are delivered to the Principal Investigator through the INO data system.

Target of Opportunity Observations

The INO340 supports Target of Opportunity (ToO) observations for transient or time-critical events. Proposals requesting ToO status must clearly describe the nature of the transient phenomenon, the required response time, and any specific observational constraints. Approved ToO programs may be scheduled with priority when scientifically justified.

Data Policy

Data obtained with the INO340 are proprietary to the Principal Investigator and collaborators for a period of twelve months from the date of delivery. After the proprietary period, data may become publicly accessible through the INO archive in accordance with observatory policy.

Acknowledgement in Publications

We kindly ask authors preparing a paper using INO340 data to notify the Iranian National Observatory in advance of the publication (ino@ipm.ir), and to provide proper acknowledgement to the use of the INO340 in any published papers. Please copy the following paragraph, updating it with your proposal reference:

Based on observations made with the INO340 telescope operated by the Iranian National Observatory (INO340 proposal(s) XXXXXXXX-XX).

Proposal Submission

Proposals must be submitted electronicallyProposals must be submitted electronically via email using the official INO340 LaTeX proposal form provided with each call for proposals. The submission package should include both the completed LaTeX source file (.tex) and the compiled PDF version of the proposal. All proposals must be sent to ino@ipm.ir

A complete proposal consists of a scientific justification, a technical description of the requested observations, a target list with coordinates, the total requested observing time, and full investigator information. Additional sections such as calibration requirements, scheduling constraints, and backup programs must also be completed where applicable.

Proposals received after the stated deadline will not be considered.

Proposal Template

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The INO340 Telescope

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